Smokey the Jeep

Hi All,
First time poster and first time Jeep owner.

Last June I purchased a 1999 Jeep Cherokee (XJ) 4.0L I6.
Shortly after purchase I noticed that at low RPM (usually going 25mph or less) the Jeep would struggle to accelerate then there would be a popping sound and the Jeep would surge or buck. The check engine light came on and I had it checked. The code read bad O2 sensor. I had the O2 sensor fixed and the hesitation/surging problem stopped for a few months.

I just had my oil changed, put in a new air filter, put in a new battery, put in some power steering additive and now the hesitation/surging/bucking is back. No check engine light this time.

Not sure what this is. It's not a sensation I've ever experienced with a car before. Any help would be much appreciated!