1998 GMC Jimmy Nightmare problem!

I have been having an intermittent electrical problem. My gauges will just go out and dash lights. I will be doing 60 and the car will miss a little, but keep going. The gauges will jump back up and the car will do a systems check while I am doing 60. Today I started the car and no gauges and a service engine code for component slipping in transmission. Nothing is slipping, but that code is stored and keeps coming back. Today after I started and got no gauges, I shifted into gear and I got the gauges back and a service engine code(the slipping component again and I drove to work with no overdrive) Tried to have a new BCM installed that I bought online to no avail, but the car was nice and warm and dry. Drove home with the code gone, overdrive, and all my gauges. Happens most after a car wash when it goes down to zero degrees.