new owner of a 93 xj with some issues

hey everyone :wave: i recently moved from Iowa to South Carolina, and had a 93 4.0 I6 2 door XJ waiting for me (a friend in North Carolina got it for me, did some minor stuff for it; replaced some seals, balanced tires, changed oil and fuel filter.) with the exception of shaking around 55 mph (possible death wobble?) it drove the 3 hours back to SC without any issue. recently, I've been noticing the engine is skipping or missing, but only occasionally usually at slower acceleration. i changed the plugs and wires, and tomorrow plan on looking at the dist. cap and rotor for wear or corrosion. today, driving on the highway back from Augusta GA, i noticed it would smoke (white color) for about 20-30 seconds, then quit for 3-5 minutes, then smoke again. i checked the oil, and it's a nice clean amber color, no sign of water, and also checked the coolant res. it's dirty but no sign of oil. i thought it might have been bad gas, but my brother-in-law filled up at the same station a day or two after i did, and no issues. ill also add, the engine was replaced around 20k miles ago. with some rust on the floor board behind the pass. side front seat, and the above mentioned issues, the jeep is in great shape with only 130k miles on the body. any advise is very appreciated.