Duramax 65mph limp mode???
 

after driving my 2004.5 duramax (138k miles on it) 50 miles or so, it goes into limp mode (65mph/ 2k rpm). it does it with or w/o the hypertech programmer on it. i have had the race valve changed and had the fuel pressure regulator changed, and i just tried the ice pick fix, but it's still doing it. around town it drives ok, although not the power it should.. the dealership says they think it could be an injector but don't know for sure, while another "good" mechanic says possibly its the fuel pump, i can't afford to be throwing parts at for their "guesses". although no check engine light on, i'm still getting the following codes...p0101,p0401,c0035,p0404,p0670,c0040,p1093. need advise guys. thanks

going off of the codes you listed starting with p1093 (low fuel pressure during power enrichment) i would put a new fuel filter on and see if that one go's away...the p0101 (mass air flow performance) that one i've seen just come and go for no reason on some llys during cold weather....p0401 is an EGR code (EGR flow insufficent)...have you done anything to the EGR like put a block off plate on?...if not then sounds like it is possibly stuck or clogged up?....couldnt get some of those codes to come up but i'm wondering if they are possibly injector harness...LLYs have harness problems on #s 1 and 7....when they go bad it causes the engine to drop all 4 on that side....be way down on power and will sound like a little tractor running...lol