Duramax diesel trucks problems

It sounds like a lack of fuel. blocked fuel filter or lines?

change your fuel filter

No, you are not able to turn up the turbo on a 2003 Chevy Duramax Diesel, but you can add modifications to increase power.----------------------------------------------------------------------------
autel maxidas ds708

Did the check engine light come on ?
Could have been a restriction in the fuel line or a problem with the throttle position sensor among other things.

if the leaks are not evident in the engine bay , it could be the heater in the cabin

Diesels only need basically 3 things to run.
1. Air
2. Fuel
3. Compression.
If one of the 3 is lacking performance would suffer or completely keep the truck from starting.

Sounds like the PRNDL switch on the side of the transmission. Be sure and clear the code before trying to start after replacing it.

I've tried one and found NO DIFFERENCE. Waste of money in my opinion...

Problem with Diesel Fuel System. Gmc 2002 duramax 2500 HD 4x4 will start 

My guess is injectors. The early duramax's had a lot of injector problems. They sometimes get to where they bleed constantly, and sometimes they break off... bad stuff. Check your oil for diesel. When my dads injectors when out on his 01 D'Max, his truck would run ok for a while, then lose power. Computer will cut power when it picks up an injector problem. BTW, Sightseer, diesels dont have spark plugs, however, the diesel filter is a good idea, you have to change them pretty regularly on the D'Max engines ( in order to try and prolong the injectors lives, mainly, the smallest bit of junk in your fuel can screw those early injectors up quick) I think they got the injectors mostly straightened out in the 04 models, what I've heard is thats the best model Duramax there has been, fuel economy, power, and reliability. Too bad all the year models arent that way :/