i know your gonna say "replace fuel filter", however, it was changed two months ago. its an '05 LLY, k&n replacement filter, and 4" turbo back exhaust which i just put on 3 days ago. what happens is, you step on it and you dont really loose power, it just doesn't really have any power, it almost feels like im driving a non-turbo diesel. the check engine light stays on and wont shut off. i tried disconnecting the batteries and cleaned the mass air sensor, and nothing works. the light stays on. any ideas?

You will have to pull a code. If no code reader go to auto parts store and have them pull code for you. Come back and report. Could be many,many things.

Check the intake piece on top o the motor that says 6.6L duramax on it and make sure u tightened the clamps good or maybe u bumped it and it popped off

My guess, if you just put a turbo back exhaust on and then the code and CEL appeared...I would place money on it that its a low boost code. I can't remember which one it is off the top of my head, but A) fill out a signature so we can help you diagnose your truck with the mods you have on it, and B) get the code read and post back.

Smoke from the exhaust? Will rpm go over 2000?

Don't want to sound like a broken record, but codes make thing much easier.

these are the codes that came up...
P0299-turbo underboost
P0401-insufficiant EGR flow
P0404-EGR feedback signal out of range

so...any ideas?

You need a EGR blocker plate and a finger stick.

what is a finger stick...and where do i get them both?

http://www.kennedydiesel.com/