Now almost everytime I drive the truck it seems to get worse and worse. I pulled out in front of a car today on accident and had to give her the beans....... After I reached about 35 mph I let of the pedal and the engine started to lope. It went from 500 rpm to 750 for about 10 seconds then stoped.

It will do it almost everytime.

Here is what I have done so far. Droped the tank and cleaned the pre-filter on the sending unit. Removed the fuel heater bowl and cleaned that pre-filter as well. Install a new fuel filter.
The throttle cable and linkage was replace already.
I know I have good fuel because my ISX is running fine on it.

Tomorrow I will : check vacuume on the fuel line before the lift pump. If all is good there
I don't know what else to do

 

what tranny

 

auto trans

 

is it jurking when it happens?
your trans could be going out

 

no it doesn't jerk. I cant feel any thing

 

maybe fuel pump getting weak, when under load you might be getting pretty low on fuel pressure then air cavitates a little bit and lopes untill its pushed through. i had an old ford idi that did this exact thing from a bad fuel pump.

 

thanks

 

I would look at changing the overflow valve first - get it from Cummins and make sure its a Basche one.

If that doesnt help, check fuel pressure.