Transmission Crazyness
 

OK folks got a crazy one here, this is on a 1993 vette and has to do with the automatic transmission. When starting up the car and start driving all gears work as they should and a good lock in each gear. However after between 10 to 15 miles of driving in town stop and go when the overdrive locks into gear after 5 to 10 seconds it down shifts back to 4th gear. If you give it a little gas the Overdrive will kick back in but again will drop down to 4th when it gets to the new speed. None of the gears slip or shift crazy in any way. Could this be the TV cable out of adjustment or could it be electronic with the lock up? Oh one other thing in the morning when the outside temp is lower it takes longer for this to start than say in the afternoon when the temp is higher so the driving temp seems to have something to do with it in some degree. Any help or advice would be great, thanks.