1999 dodge cummins diesel

My truck runs starts and runs fine until it reaches high gear where it begins “bucking”, surging as if the throttle were being pressed then let up many times.

Having been told the transmission was bad I replaced it to no avail. The truck still bucks like a wild horse.

I now think it may be some electronic component which is malfunctioning such as a speed controller but do not want to spend millions of dollars for a dealer to “guess until we get it”.

There are no codes.

help help help

Have you changed the fuel filter(s) recently?

Thanks for the reply. Yes the fuel filter is OK.

I am a retired interstate trucker and am used to C12-13, Detroit 60…etc The symptom of a clogged up filter is gradual loss of power at speed.

more info here: The bucking is between 200-400 rpm and it is not downshifting.