check the cap for water or corousion

I don't see cap or rotor listed as being replaced. As answered before, check for water.

Did you ever resolve this issue? I'm having the same problem on my 2000 S10 2.2.

I would recommend checking your battery ground by adding a heavy gage grounding cable temporarily in parallel with the existing cable to see if the decreased resistance to current flow into the ground side of the battery reduces or eliminates the misfire when it rains. My thought process is based on experience with a 1986 F150 that had a few broken strands hidden inside the insulation of the ground cable. The nuts were tight, but the loose wires inside caused misfire when wet, and no fire when hot. Also, the resistance was fine cold and dry. Since there is no distributor, it would help to understand how the coil packs work on the 98. Cylinders 1and4, 2and3 are paired electrically on their coils. While one is exhausting at high temperature, the other is compressing and builds higher voltages across its spark plug gap. This causes it to fire its side of the coil instead of the exhausting cylinder spark plug. Water in the intake air slightly decreases the spark voltage buildup in the compressing cylinder and is also a little harder to ignite. This engine has already been tuned up fairly high compared to its low HP predecessor the Iron Duke 2.5L. It is easy for small problems with grounding to kill alternators and cause ignition problems.