Bucking at speed

So I recently bought a 1999 XJ limited 2wd 4.0L with 130K miles on it. It has the chrysler 8.25 in the back.

When I am going 45ish up a hill the whole car starts bucking violently. When I put it into 3rd it mostly goes away but still does it a bit. The rpm's dont change during the bucking and I can accelerate out of the bucking, as in if I punch the gas the vehicle will accelerate and stop bucking.

Also on the highway when I punch the gas there is a single knock noise and then the vehicle accelerates.

I am leaning to something wrong with either the overdrive or the lockup part of the torque converter.

Any other suggestions.

Thanks

Owen

1999 XJ limited 2wd 4.0L Chrysler 8.25, 130K miles

Last time mine did that it needed spark plugs, and a new cap and rotor.

Get an OBD-II scan for pending codes at a local parts store for free. Pull the spark plugs and check them, post up pictures if you need help, Google the spark plug condition guides on line.

Mine did that...changed out CPS. Fixed.
Mine never gave any codes or pending codes.

Are you able to use the on- off flash code method with a 99 and rest the fault codes. done this plenty of times on our 91 and 96 and always gave me a place to start looking in regards to problems.

I'd check the Throttle Position Sensor (TPS) throughout it's sweep with an ohmmeter.

You probably have an engine or sensor issue causing a misfire, and not a transmission issue.

As suggested, are all the tune-up parts fresh ? Tested the coil ? Tested the fuel pressure ? Tested the Coolant Temperature Sensor ? Cleaned all the ground wire connections ? Considered that the Crankshaft Position Sensor may be failing ?

Use an OBD-II trouble code checker, and look for any stored codes.