fuel filter light while driving at constant rpm's of 2000 or higher

[a_higg7.3]

I have just recently brought this truck back from its shallow grave. It is a 96 f-350 crew cab long bed dually with the 7.3 turbo. It had not run since 2010. I had to put a transmission in it and a steering box some batteries and other misc. parts. So it cranked up within 30 minutes and runs fine. i drove it around all weekend, then finally decide to take her home, to get inspected. While driving around 2300 rpm's or roughly 70 mph the fuel filter light comes on, the truck bogs down and tries to shut off. I shift into neutral take the load off and it idles rough shaking the entire truck back and fourth. It clears up and I carry on down the road. Then does it again and again and again... At slower speeds around 1200-1500 rpm's the truck does fine. The truck used to run on a mixture of things. Burnt transmission fluid mixed with diesel and a little gasoline. Is it possible that gelled up in the lines or the pump or anywhere? Also I did change the fuel filter. Thanks for any advice. Also I am new to the thread and this truck, so I may not know all the technical terms.

[LeoJr]

Did you change the fuel filter? I suspect it is so clogged with gunk it won't pass enough fuel to run at the higher RPMs.

The harder fix is if the low pressure side of the fuel pump is weak and can't push enough fuel into the filter bowl fast enough for the higher RPMs.

[a_higg7.3]

Yes I have replaced the filter. It still does the same thing after the replacement

[LeoJr]

Is the oil level good?

[a_higg7.3]

Yepp oil level is good, had one of my mechanics test drive it at the shop today and it died. Now it will not start up at all. I am replacing the fuel pump and going from there.

[a_higg7.3]

I replaced the fuel pump and she is running great now. Also doing some fuel and stiction treatment.