2004.5 lly Duramax 3500 srw Ally automatic, I was towing my boat home after a tournament and going up the mountain pass I had no power. I had my foot down and it slowly lost speed, dropped down a gear smoked like a chimney and got me back up to speed, shifted up and then lost speed again. Made it home ok.
Cleaned MAF sensor, new fuel filter, injector cleaner in tank but nothing helps. When driving down the street I can push the pedal but there is no power, acceleration is slow and it won't act like there is power unless it drops down a gear and even then it lags. What do ya think? injector problems?

 

Is there a code thats poppin up? anything? sounds like it could be injectors but idk for sure

 

I'd suggest check fuel pressure.