Auto Transmission slow to engage after sitting a few days

Anyone experience their auto transmission not wanting to engage after the truck has been sitting a few days? I have a 1999 Tacoma extended cab that I bought used with 80k on it. I changed out the tranny fluid thinking that would fix it, no joy. I ran it for about two months and then switched everything out to Amsoil hoping that would clean up whatever was dirty, but alas still no joy. I haven't seen any recalls from Toyota on this but I hate the thought of pulling the tranny, once the truck warms up and it's been driven it works fine until it sits for a few days.
Thanks in advance for any help.

 

Something (checkball, solenoid, etc) is sticking. Take it to a shop that specializes in trans repair and overhaul to have it diagnosed. 80% of problems can be found and fixed without pulling the trans.
Good luck, and keep us updated.