03 Transmission shifting problems

i was wondering if anyone could help. I have an 03 AWD V8 5 sp Sport with 50k mi. A couple of mornings (always less than 55 degrees ambient temp) I noticed the transmission will not shift past 3rd gear. The first time, i pulled over and went to park, then back on the road.....nothing. Then I pulled back over, went to park, shut off engine for a few seconds, started, and it was fine. A couple weeks later same thing. Stealer said at first, that it holds back a gear to warm up....but this was 2 gears and it would only go away if i shut everything off.
Any ideas? I'm thinking it's a computer problem/glitch.

Also....a few times i've went from drive to reverse to back in to garage and it takes quite a few seconds to engage.