maachine

so a few months ago i posted a thread about my trans slipping. i ended up changing the fluid and it seemed better. i disappeared for a while for work and my daughter's mom and my mom both used my truck while i was away so it wouldnt sit. so the other day, after sitting parked and idling for a while, trans started slipping again. hasnt done it since but eventually its going to get worse.

any ideas if it could be a bad solenoid or something......possibly an easy fix? overheating issue?
rebuild? does anyone know how much that would run? got quoted about 1000$ by one shop but that was for them to pull it from the truck, rebuild, and reinstall. i'll pull it and reinstall it myself though.