12 valve problems

[BigBad80Dually]

I am having a problem with my 95 12 valve. It runs good 70-80 mph on expressway. Then all of a sudden ill let off the accelerator and it accelerates really slow seems like it doesnt have any power and will only go about top speed of 50 mph. Ive recently did fuel heater delete changed fuel filter changed fuel pump overflow valve and im still hacing this problem. Then once i get to where im going and i turn it off and then i get back in it it will run fine again. Does anybody have any ideas of what it could be?

 

[kino_fab]

fuel shut off getting weak possibly, cutting off half the fuel after a hard run. Try it agian but instead of shutting the truck off after it does the slow acceleration, raise the hood and see if you can pull up on the shut off lever. If it moves, take it down the road and see if that helps.