i have a 1995 3500 cab and chassis with a 12 foot flat bed.i bought this truck in texas and drove it home every thing was great after about 2 weeks the truck lost alot of power and i can't seem to get it back also fuel mileage dropped.when we looked at the truck in texas the airfilter was all wadded up and the rubber around it was coming off,we replaced it after the test drive and drove it home to tennessee without a problem.the does not seem to make any power above 1800 rpm.i have put an turbo back exhaust with no cat,TST #5 torque plate,air raid cold air intake,LUK 13" upgade clutch kit and flywheel,changed fuel filter and cleaned the prescreen filter.when we took the hose off the turbo we found some of the orange fram rubber from the wadded fiter in the silencer ring.i usually have 10,000lbs on the truck so i need all the power i can get.

 

Maybe something from that old filter is clogging up your intercooler. I'd take it somewhere to have it cleaned and pressure tested if you even THINK something might have taken a ride through the turbo. Also, pull your intake horn off and see if the pre-heater grids may have caught any floaters. Only other thing right off the top of my head would be the governer arm was not adjusted properly when the #5 plate was installed. Keep us posted.

 

I agree, look for junk in the intake system, the gov. arm, check your turbo boots for leaks and holes, in addition replace rubber fuel lines, check out/replace your overflow valve, and get some gauges so you can see what is happening. Boost gauge and egt gauge are a must with a modded engine. Consider a fuel pressure test as well, as it will help you diagnose the overflow valve and give you an overall condition of the fuel system (any leaks).

Do a search on all of the above items you have not looked at yet, get ready for lots of reading. Good Luck

 

i also installed a new lift pump and they tested the check valve

 

If it went from good to not just like that I'd say timing slipped. Is it harder to start, any difference in cold start-up smoke/runnability?

 

I second slipped timing.