2001 Dodge Ram POSSIBLE PROBLEM AT WARM UP

Right after I got a fill up at a station the day after they reopened from under ground tank repairs, my truck started to have very hard misses while driving at highway speeds. I thought it was bad gas, but the miss feels like it is cyclic on one cylinder. It will have several misses and then be okay for the rest of the day. It had several misses again this morning on the way to work at 3:00 am while pulling a hill and then was again okay. I now think that the problem may have occured just when the engine was starting to heat up, which I would have been on this hill at that time. I have replaced the spark plugs every 50,000 miles, the cap and rotor every 50,000 miles and the current spark plug wires have 100, 00 miles on them. The fuel line filter was replaced at 100,000 miles with the electric fuel pump being replaced at the same time. Any ideas?