I can't drive 55
 

Hello Everyone!
Heres what's goin on. 94 1500 Magnum. When you get up to 55mph and try and hold that speed it starts buckin, can't tell if it's the motor or transmission. Now, if it's under a load like up a hill or accelerating it will not duplicate, but on a decline or trying to hold 55 on a level roadway it will shimmy and fight me. you can play with the throttle by letting off a little and find a sweet spot but is super irritating.
-thank you for any and all input, Kevin

Would it possibly be tranny trying to shift all the time? I'm not sure but sounds like a possibility, that your rpms are right in between 3rd and overdrive and it can't decide which to go into

Misfire?

i would like to think it is fuel related. possibly a t.p.s or an injector. the transmission is goin on me. not liking 1st or 2nd gear. but like i said I can't tell. hopin someone has experienced the same prob. before.

Problems I have already had
- intake plenum - repaired
- head job 6 months later
- fuel pump - scotched locked a 2001 fuel pump into the harness
- overheated motor - bad sensor - actually locked motor up but was able to free it loose and subsequent head job followed
- broke cardinal rule - changed tranny fluid well after 60k

One last thing I forgot to mention. the intake tap off the exhaust manifold does not have a good seal and also a couple pin holes on the dump before the cat(which is hollowed);)

Sounds like misfire. When was the last time you checked your assorted ignition parts? (cap, rotor, wires, plugs)

+1 on ignition parts.

And WHAT does "tap off the exhaust manifold does not have a good seal" meanin English?

My guess is the egr tube.

You seized the motor by over heating it, I would start with a comp test and see what's up.

+1. When engine gets overheated, something usualy fails. When it locks up it is usually the result of whatever failed, warped, etc.