IS ther some sort of acceleration limiter or something in place on the duramax? Recently my truck will quite often stop accelerating at 65mph, always right at 65mph. It dosnt seem to be transmission related. It is as if it just wont let me accelerate over 65mph. It usualy dose this after I have been driving for a while. Any ideas?

Rick I did a little searching around the net and found a lot of info on what you truck seems tobe doing. Try googling "duramax limp mode 65 mph" several results come up. You can read a little more about it here as well. http://www.motownmuscle.com/forums/showthread.php?t=8932

Maybe some more people with experiance will chime in.

Check the truck for codes.. It sounds like a limp mode.. You dont have any programmers on it do you?