Manuellabour247

Have you pulled the rear diff cover or drained the fluid to inspect the gears as mentioned earlier?

Carcrazygts2

First of all your truck doesnt have a 5th gear. It has a 4 speed transmission. The issue you are feeling is called torque converter shudder. You need to have a trans service done. Which includes a new filter and premium synthetic fluid. No cheap crap fluid. You will also need a bottle of a specific kind of additive. Its made by Lubegard. Its name in Dr.Tranny Instant Shudder fixx. You will need 2 tubes of it..

TLB4

If it's bucking right at low RPM in the higher gears, it probably is a sparkplug or two misfiring. I had this issue for a long time on my standard 4.2l V6 before finally figuring out what it was. It would only do it under high load at low RPM's. It wasn't misfiring enough to throw a code. Ended up having to hook it up to a ford data logger and take it out and watch the graph to even see it doing it.
I ended up changing the wires while I was at it too.
Bucking on these trucks is a common issue, there are tons of threads about it.

hendricksn

It runs fine otherwise. Any way to test and confirm this?