Toyota Repair: toyota temperature, shifting into overdrive, toyota corolla

Question
Hi, I have a 94 toyota corolla that has a couple of things that are puzzling me recently..The first is that in the morning, when I start the vehicle and let it warm up initially, it will warm up fine, heat blowing into cabin wery well, but, when I start driving, the temp. gauge starts to go down and the air from the vents starts to get cooler...not cold mind you, but not as warm as if is sitting still...when i pull into the lot at work and sit, the temp goes back up to normal, and the heat increases coming from the vents........the second question is, the vehicle  has a habit of not shifting into overdrive until it has reached a specific temp..or that is what it appears...in the summer, I would have to drive it for roughly 10 minutes on the highway befor it would shift into overdrive..Now that it is much cooler outside, it takes about 30-35 minutes of driving before it will shift into overdrive.....any suggestions?...what should I do ?......thanks....PETE

Answer
Check the engine cooling fan, when the engine is cold it should be off, turn the key on and see if the cooling fan runs all the time. The transmission is designed to not shift into O/D until the engine is warmed up, taking to long to warm up could be due to a stuck open thermostat or a cooling fan that stays on all the time.