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1996 K2500 ext cab, long bed, auto trans, 3.73 gear, 200K miles. Added home made wastegate spring set to 12psi max, no other drivetrain mods, everything else stock as far as I know (bought the truck about a year ago). Truck seems to run fine, doesn't have excess blowby, doesn't smoke ever. No idea when the last injector/pump service was done on it, and I haven't done it since owning the truck. Have thought about it, but it's a lot of money to throw at the truck, "just because". I'm maybe it's time to throw a new timing chain set on it, and bump up the injection timing a bit?

I don't know if my truck really IS having issues, or if this is just the way these things are. Having never done a trip like this before, or really ever towed anything with this truck, I don't have any good frame of reference other than comparing it to my 1990 F350 with the 7.3 IDI & Banks Sidewinder turbo set to max at 15psi, but even empty, these trucks feel like they're in completely different classes power wise. The Ford feels like it would pull 15K up a grade better than the Chevy would pull 5K on flat ground. I know the 6.2/6.5 engines were never designed as towing/hauling powerhouses, but it seems like this truck should have more in it than I was getting out of it yesterday. I bought the Chevy to replace the Ford when it developed some major oil leaks, and the AC went out last summer. At the time, I was over loaded on other projects, and it was just easy to buy another truck.

Went from home in Phoenix to Tucson pulling a 2500lb empty bumper pull flatbed trailer, picked up a 3300lb car, so total load just under the rated tow weight. Phoenix sits roughly 1300 feet lower in elevation than Tucson, so it was basically a downhill run the whole way back.

I had Torque Pro running the whole time there and back. TDCO is currently -0.9. The way down with the empty trailer, cruising at 75mph - was showing 15* cam timing, 200* intake temps, 185* coolant and trans temps, 750-800* EGT, 5-6lbs boost.

Seemed to start out OK, but after about an hour on the interstate, the truck really felt down on power, and would barely muster 70mph going over overpasses, foot to the floor. At first it was just an issue of keeping it from defueling from overboost, but about 2/3rd of the way home, it was all it had to make 60mph up even the slightest incline. Defueling wasn't an issue, as it couldn't even get to 70mph. I'm perfectly content towing at 65mph, I'm not expecting it to do 80+, or was even trying to, but did notice the drop in perceived power when accelerating from slowed traffic.

By this point it's running a near constant 8-10lbs boost, 65mph on flat ground, I feel like I'm really far into the throttle (though I didn't have throttle percent showing on the logger), 205-210* coolant temps, 200-205* trans temp, 14* cam timing, 235* intake temps, AC running, outside air temp 100-105*. A few moments it creeped over 210* coolant temp, and I turned off AC to bring it back down, but it was still 200+ almost the entire way home. Came down to 190-ish when I got off the interstate, but even still, it pulled out from a stop very slowly, and was very slow to build boost, only peaking around 7-8psi. It FELT like the ECU was pulling back a lot of fuel as the truck got hotter, similar to what happens when it sets a overboost/defuel code, but it wasn't setting any codes.

It never seemed to run weird other than a seemingly huge drop in power. Like I went from a 200HP truck to an 80hp truck. But as I said, no frame of reference. Maybe this is normal for these things? I'm not trying to make it like my Ford, I'm not trying to make it some kind of beast of a power house, I'm not necessarily looking to throw a bunch of upgrades at it, especially not without knowing if I have a good baseline first. If there's other issues I should be looking at first, I'd want to address that before changing things anyways. This is really just a parts chaser/tow rig for me, and I'd never see a return on thousands worth of upgrades.
 

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What was your fuel pressures during that time?
 

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To much info. Has the soot trap been removed? How much are you pulling and how far? Temps are hot now so cleaning radiator inside and out would be a wise move.
 

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Discussion Starter #4
My apologies. I was unaware that the preferred way of asking for help wasn't to provide details, but rather to just say "truck not running right..what's wrong?"

Sorry for wasting everyone's time.
 

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Not wasting time, just to many vehicles in the explanation. Care to answer above questions? Lets just get a few at a time and go from there. A new sock in the fuel tank would also be a good place to start with a fuel pressure test under load..... you'll be shocked on that test.
 

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10-12 max psi for boost will cause defueling.

Do you have a EGT gauge?
 

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Sounds to me you may having fuel pressure issues. Its been asked a couple of times in this thread. What iis fuel pressure? Maybe time to install a fuel pressure gauge? So you can see what is going on in the fuel delivery system.
Have you checked for air in fuel?
What about your fuel filter.? Is the fuel cap venting properly? Lift pump working? Also to ask again Has the soot trap/ Cat convertor been removed? If you have one it may be plugged.
Besides boost pressure. OBD2 engines use intake air temp for fueling. If intake air is too hot they will de fuel. A plugged exhaust will cause high IAT from heat transfer thru the turbo. Best to have a good free flowing 4" exhaust.
 
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