2002 Duramax 4speed auto
injectors replace

It runs normal and drives fine, but when driven at 70mph
it will act as if you let of the gas, but it is still to the floor!
Holding it to the floor, it proceeds to slow until stopped.
once stopped, put it in park and shut it off, restart and it goes again! Now it has been to the dealership for 4wks and they sent it back saying they don't know what is wrong with it.
really appreciate feedback!

If it was fine before the injectors were replaced I would go to the dealer and demand it fixed, If they dont get it right this time, they owe you a new engine or maby even a new truck. That should work, when randy (buddie who runs cattle) has problems he lets them know he means business (once punched a smarta$$ d-max tech, knocking him out) and sure as hell the truck was perfect when he picked it up the NEXT DAY! (they replaced the whole front running gear, suspension, and hardware.) oh and they washed it and filled his tank for him too.

It was fine after receiving the truck, and good for months
then this!

Try a different service department?

I would check the electric foot throttle. It may be shorted out part way thru it's motion.