I have a 1998 Chevrolet Silverado that is not shifting into overdrive. It is throwing a code which says that the 2-3 Solenoid is bad, but an auto electrician told me it wasn't bad. I dropped the pan on the transmission today to check and see if the solenoid was still in place and went ahead and changed the fluid and filter. I recently installed a new pcm and that is when my problem started. I had it flashed at the chevrolet dealership and it hasn't shifted into overdrive yet. Does any body have any idea what this could Be?

 

Put the original PCM back in. See if the code returns. If code returns its probably a wiring problem ( short or rubbed wire). Is it 3-2 downshift solenoid code or a 2-3 shift solenoid code ? it matters, different parts. Need more info to help you.