I know my truck is getting a little long in the tooth but no cash for a new one so this unit will need to get some help. First it's 1998 3500 dually 6.5l turbo. 125k miles. No aftermarket stuff. New injection pump last week, new lift pump last month.
My problems are poor fuel economy (10 mpg not under load), lack of power, hard starting when cool. None of the above are really serious but need some attention. I know I need some guages for monitoring but what else. Everyone can chip in their two cents because right know I'm knowledge broke. Thanks.

I am guessing you have 4:10 rear gears, what size rear tire? What is your usual cruising speed? Reguardless, 10 is a bit on the low side. First thing to check is the vacuum operated wastegate. Low power and poor mileage could be a bad vacuum pump, wastegate solenoid, or associated plumbing. A boost gauge would diagnose this problem quickly.

Was the pump NEW or reman, sounds like you got the 'NEW PUMP BLUES'. A lot of complaints about newest issue of 5521s for some reason.

hard start can be fixed by checkin glowplugs. one end of test light on + of battery, touch the end of glowplug. if it lights its good.

gauges, exhaust, turbomaster

Right you are Steiner but just to help paint a clearer picture. You need to touch the spade where the wire connects. Be sure you disconnect the wire before testing or it will find ground from the other glowplugs

Dr. Diesel

P225/16 is the tire size. Usual speed is 60-70mph. Put a new wastegate solenoid on a couple weeks ago. Should probably check vac pressure. The fuel mpg was the pits before changing the pump so there are other problems. It seems I can only hear the turbo whine when the motor heats up (when pulling the trailer) to around 100c. How do I install a boost guage?

Find a nice spot on the intake somewhere, drill and tap to fitting size in kit and install fitting where the tube won't get pinched, run tubing to where you decide to mount the gauge. Nice and easy

Check your air cleaner, check turbo impeller for excessive clearance(impeller should not be able to touch housing, check after engine has run for a few minutes to be sure that the turbine shaft has some oil around it.) How old is your fuel filter?

Air cleaner was changed last oil change. Have put three fuel filters in the last two months. The last one was done with the injection pump this week. It's has to be that the turbo is not working correctly. The only thing it could be is the vac pump. I have pressure there but maybe not enough. Why does the turbo seem to only kick in once the truck is under heavy load and starting to heat up?

What are your Vac readings at different spots in the system?