1995 Chevy k1500 4X4 350 run problems when cold and wet

I have a 1995 Chevy k1500 4x4 350TBI 111,000 miles. I have owned it for about 12000 miles. This winter it started acting up on days when it was cold and wet (not just cold, nor do I remember it when just wet, but of course winter time is usually both.) While the engine was cold, for the first few miles down the road, the rpms would drop 400-700, the engine would become sluggish, and then would return to previous rpms. When this began, stepping on the accelerator would restore power and acceleration. When holding steady or only slightly accelerating, this cyclic phenomenon would persist until the engine warmed up sufficiently (and I assume dried out.) The first time this occurred was on cold foggy day, but has continued to occur. Two days ago the problem stepped up. My wife was driving, another cold, soggy day of snow and slush, and she had problems accelerating at all. Just getting up to 20 mph was a challenge. When it warmed up on the expressway, it seemed to do fine. When she arrived in our city, the car started acting up again. This is the first time that it did it once the car was warmed up. We finally got an engine light so I thought the code would help me, but didn't. 45 is the code is showed, running rich. I took it out yesterday and it did the same until warmed up, then ran normal. Holding the accelerator steady, at say 25 mph and 1500rpms, it would drop to 700 rpms then return to 1500 rpms for 20-30 sec. And do it again. Connections and wires appear good. I have pulled several connectors, checked for corrosion and replaced them. Airfilter is clean, oil pressure good. Any suggestions as to where to search for the problem? Thanks.