Truck surging

[smokeyd]

I have a automatic in a 01 7.3 and it has about 40k on a rebuilt trans. The other day I was driving down the road and it started surging, the rpms stayed the same but the truck would lunge forward and then nothing then lunge forward and sounded like the motor would quieten down then roar, rattle, up then quieten down during this. I kept driving and it seemed to correct itself. Last night i was pulling a big horse trailer and 5 horses and it started doing the surging or whatever real bad, i took overdrive off and it corrected the problem almost completely. Any ideas guys??? torque converter? Transmission? motor? lol im lost as last years easter eggs.. Thanks for any opinions!

[Austinj427]

Have you checked fuel pressure?

[smokeyd]

No I haven't, I guessed it was transmission related since it stopped kinda when overdrive is off. Maybe it doesn't do it as bad when the rpms are up

[smokeyd]

bump for the morning folks

[smokeyd]

ok its doing it bad now, It felt like someone was rear ending me on the way home tonight, i threw it in neutral and it was still doing it so possibly tps??? i had to change it out a few months ago but used one from the junk yard, think that could be the problem also???