My truck is a 97 GMC K2500HD. It sat for most of the winter and now I'm having some problems with the truck "bucking" intermittently while driving at various speeds and loads. Back in the fall when I was driving it more regularly it would only buck and chug under hard throttle but now it's doing it while I'm just cruising around town under light throttle as well. I want to sell the truck but when it acts up during a test drive you can imagine the prospective buyer is NOT impressed. It has also developed an intermitten clutch problem where the clutch will work fine for a while and then randomly stop disengaging while stopped at a light or something like that. I've got a feeling it's got a throwout bearing issue or maybe a slave cylinder on it's way out the door but I can't be sure until I drop the trans and see for sure. Anyways here's my checklist and any insight would be much appreciated. (I'll update the parts I skipped over as soon as it quits pouring rain outside)

0. Describe in detail the problem you are having. Please be as descriptive as possible.
1. Does the engine crank, or 'turn over'? yes
1a. Does the engine start and run? yes
1a1. If the engine does not start - Crack injector line (http://www.dieselplace.com/forum/showthread.php?p=2188140#post2188140): do you have fuel? Yes/No
1b. Do you have a Wait To Start Light & the amount of time (seconds) lit. yes/ lit 3-5 seconds
1c. Ambient Condition (temperature outside indicate F or C) _65____ °
1d. Engine Cranking speed (if you have an accurate tachometer).
1e. Are you experiencing stalling? yes
1f. If Stalling, describe (upon startup only, down the road, hit a bump etc) intermitten while driving
1g. If Stalling, do you notice loss of dash or instruments? no loss of instruments
-note if experiencing stalling,you must indicate PMD location in #24.
1h. Check turbo inlet and air filter for obstructions. Cone filters have lost disk and stopped air to turbo.
1i. In a no-hot start, pour a bottle of room-temp water on the injection pump. Does it start now? yes/no
1.1 Lift pump test (http://dieselplace.com/forum/showthread.php?t=39350)- describe results. lift pump replaced, does not run consistently upon turning key to ON position, but does run after repeatedly turning key off and back on.

2. Service Engine Light while running?- off
2a. Service Engine light does glow during start/cranking/bulb check: Yes
3. Model year 97
3a. Odometer reading (indicate if in miles or km) 250,889mi.
3b. Miles on major engine components if been replaced (example Injection pump)
3c. Indicate the model number on the Injection pump (starts DS4 or DB2......)
4. Have you scanned for engine codes? (varies by pre/post 96) no
5. List exact results on engine codes (http://www.dieselplace.com/forum/dtc.php):
6. Air Filter condition (visual check) slight discoloration from dirt.
7. Fuel filter condition (freshly changed/condition unknown/mileage since changed) freshly changed
8. Condition of Battery terminal connections (removed, cleaned and tightened) good
8a. Known condition and age of the batteries. New condition, 4 months old.
8b. Are batteries of differing age or are they a matched set? matched set.
8c. Condition of Major Grounds (http://www.dieselplace.com/forum/showthread.php?t=157085). (same drill as batt - removed, cleaned, retightened) good
9. Upon cold start, does the radiator hose get hard quickly? no
10. Upon cold start, do you have excessive white smoke? no
11. Do you have excessive cranking time before the engine starts? cranking time has increased recently on cold start, ruled out temperature as cause of hard start. Once engine has run for 5 minutes crank time returns to normal.
12. Have you used the block heater, and does this effect engine starting?(only try for starting problems) no
13. During hard acceleration, do you have excessive black smoke? no
14. Do you have any unusual exhaust smoke issues? no
15. Turbo check out (http://dieselplace.com/forum/showthread.php?t=39368)- pass/fail
16. Do you have an EGR on the engine? (An F or an S engine code 8th VIN digit) F code
17. Indicate if you know if it’s a 1500, 2500, 2500HD, 3500, 3500HD. 2500HD
18. Indicate fuel that you are using: Bio-diesel, #2 Diesel, #1Diesel, SVO/WVO, other #2 from local truck stop (low sulfur 500pp max)
18a. If running a VO (Veggie Oil fuel) setup, indicate details of your conversion (homemade, or packaged system)
19. Are you using any fuel additives? If so, please list. Diesel Kleen every fuel stop.
20. Please indicate geographic region you are in: (example: Texas or Canada) North East Ohio
21. Do you have any service history available that might pertain to the problem you are having?
22. Please indicate any modifications to the vehicle that might help us diagnose better. No modifications other than cat/muffler delete.
23. Upon unscrewing the fuel cap (http://dieselplace.com/forum/showthread.php?t=42338), do you have a large vacuum formed in the tank? yes, I leave the fuel cap loose to prevent this.
24. Location of PMD/FSD (http://www.dieselplace.com/forum/showthread.php?t=39436)? On the pump/remoted over intake/remoted out of engine bay (please specify placement specifically) stock location PMD
24a. If remote mounted, describe wiring harness (homemade or purchased from a vendor?)
24b. Indicate the location and condition of the FSD/IP grounding wire.
25. Are ALL glow plugs in proper working order as per this thread (http://www.dieselplace.com/forum/showthread.php?t=39182)? not sure

my guess is PMD if it's original. any water in the filter? drain it while the lift pump is on and change filter if there's any. optical sensor might be reading trash(water)in the line.

Mine is doing this as well, and I have come up with a couple things that could be the problem

First, how many miles on your injectors? I was lucky enough to take mine out and go to a dealer who let me pop test them. mine popped between 1900 and 1700 psi which is in spec but low

Second, what is the condition of your IP? Did you change it lately where you couldve messed the timing up?

I have changed almost everything short of the rotating assembly and mine is still a lot slower than when i bought it and bucks every once in awile. (although getting worse) I've grown to live with it until it goes BOOOOM, then its getting a cummins or a six liter

I'm not sure about the injectors but the IP was replaced not long ago. I'll have to look up the exact mileage, it's recorded around here somewhere. No water in the filter.

No water in the filter.
that's good. can u do like jeepcj75 (http://www.dieselplace.com/forum/member.php?u=84369) and get your injs popped? there's a shop not far from me that i will get mine checked as soon as i get her on the road. is your wiring harness homemade or purchased from a vendor? have u looked at it to see if there might be a short somewhere in the grounds or wiring?

Pmd is highly suspect,as is air in the fuel supply(pre LP leak in the line at/from the tank)

Get a new PMD (less than $200) on a remote heatsink.

Also, see if there is a lot of oil in the intake before the turbo coming from the CDR valve, the gold tuna can thing.

Your LP should come on with IGN, if its not its because your LP relay is bad, check it. It is coming on from the OPS after you crank several times. can you hear LP running after shutting truck off?

I want to look into the possibility of a leak near the tank. Every once in a while I do notice a small puddle of diesel fuel on the ground almost directly beneath the fill tube. It doesn't happen regularly, and I had suspected that pressure in the tank was causing it to leak through the vent. How do I go about checking the relay, jump it across with a paper clip or something? I do not hear the LP running after shut off.

The surest way to test LP is to run jumper wires from batt to LP plugin,or test harnass up stream of LP for 12v with key on .you can jump the relay too,if you know wich pins to connect.
Leak at the tank means trouble.

To check to hear the lift pump after shutdown, do it with engine cold .That is ,start engine cold & imediately shut off while oil is cold and thick. If pump is working you should hear it run on while pressure dies off . Dies off almost imediately on hot engine .

To check the relay you can take the LP harness off, put multimeter leads to it, and see if voltage to the LP goes to 12V when you turn on IGN. The PCM does cut it off at some point, so make sure to look at multimeter in first 10 seconds.

Or replace the LP relay with one of the other relays, like headlights or something and test those.

If its not running after you shut off I would suspect the OPS as well.

Or the LP is just bad.

I'm sorry, guys, I thought I had included in my original post that both the OPS and LP are both brand new. I'm going to the store to get some clear plastic line to try bleeding the fuel system again just to rule out any air in the lines. I'm also going to try to check all the grounds to rule that out as well.

The LP runs off of the relay in your truck, so best to make sure its working. OPS is just to prime the system after shutdown.