When I drive my truck and it is below 35 or 40* out my tranny won't lock in over drive. It will start to lock up but slip right back out. I drove it 150mi. today in this warm weather and the tranny acted like nothing ever happened.

So any suggestions? I was thinking trans temp sensor. The truck does take quite a while to warm up but once it does it runs 180*.

Could it be the thermostat? It takes much longer to warm up than when I first bought it. It also smokes bad when cold kinda white blue smoke, does that sound temp related?