Rough cruising - o2 sensor problem?

Hi:
A week ago I bought a 92 civic vx. The previous owner had to put a new distribuer cap, wires, etc. and did not have the experience to do the timing. The problem is I get normal acceleration but when I am cruising at like 60 miles an hour the car keeps hesitating and just running rough. It is okay for maybe 5 minutes until the engine gets warmed up. I do not have a check engine light on. Could this just be a timing issue or maybe the O2 sensor is no good. Any help would be appreciated. John

possible a o2 sensor voltage too high. when your cruising and your vehicle starts acting up try and floor the vehicle a little while to see if it clears up> by doing this it puts your vehicle into a Modified open loop. there by it is not using your 02 sensor a a primary sensor... Possible when you first start your vehicle and it is cold the vehicle is in a closed loop and is using the ect, tps, baro, engine mapping for air/fuel ratio