I have a 93 Silverado I bought a few months back 178,000 miles. When bought it had small electrical issues like the heater would only turn on windshield defroster (no vents) only one stereo speaker worked and some interior lights didn't work. A short while ago I had a very small offroad accident were I skimmed a small tree enough to peel the front right fender back (it was already loose and smashed.) The moment I hit the tree I noticed a few electrical problems occurred, the heater quit working completely, the 4x4 light went off and speedo stopped working. next day I try to drive it and the trans only goes into 1st gear when in D overdrive, I can manually shift to second gear (2). That's it. I believed my trans problems were all electrical because of the fact that the trans shifted perfectly until the moment I hit the tree and that's when some electrical problems happened. This morning I took out the ECM, and unplugged every electrical connector behind the glove box and I did find some corrosion on some of the terminals. I cleaned everything up made sure all was plugged back in and when I drove it for the first time I put it in D overdrive and it shifted from 1 to 2 on its own no slip (good sign) but when it tried shifting to 3rd it slipped out of gear completely and went back to how it was before manual shifting to second without 3rd or 4th. all fuses double checked none are blown. was thinking just buying new ecm, any gmt400 gurus know what could fix it? Yes I saw where a couple people posted that to fix no 3rd or 4th replaced the 3-4 clutch pack but just didn't know if an impact would only cause that clutch to wear out instantly. I guess since I was in 3rd or 4th gear when I hit the tree then it could have rubbed the clutch hard?