Trans downshifts to 1st / wierdness

[robcas47]

I exhausted the search function so I am now asking for opinions and advice.

 

My 06' Silverado has started acting up. First thing in the morning I get a few minutes down the road and it down shifts to 1st and will not upshift. I pull over, shut it down for about 30 seconds and after restarting it drives and shifts through all gears normally, a Lil hard into 2nd but overall normal. If the truck sits for several hours it will do the same thing but always drives normal after the 30 sec reset procedure. My first thought was that the 3/4 clutch packs were bad bit the truck shifts fine after the reset procedure. Then I figured the PCM could be going bad so I found a replacement at junk yard and just need to get it programmed. My other thought is that it might have to do with the battery since it is occurs while truck is still in a cold state.Anyone have any thoughts on this? Any help is much appreciated

[00Silverado4x4]

Honestly, I'd get it scanned for any possible codes. In today's vehicles there is so many things that can go wrong.