Transmissin overflow?

[SoCalSlaughter]

My truck is a 1990 Suburban V2500 TH400 trans, 205 N/P transfer case. This has happen twice in the past 2 weeks, the truck is on 315/75/R16 tires, 4 inch lift. I did alittle off roading with some friends (Always get a call when they get thier little Rangers stuck haha) I do have to use the 4X4 from time to time, anyways! after getting home, being followed by a friend, we park and he comes up and says my truck was smoking, look under and it is smoking, crawl under and the transmission fluid has managed to come out of the vent tube going up the fire wall and has run down onto the exhaust and down the body of the truck some. This has happen twice after going off road. I can drive the truck to work (About 12 miles, city and hwy driving) and no problem, even drove 60 miles threw the mountains (Up to 5200 elevation) then 6 miles threw a river bottom (Didnt have to use 4X4) with no problem. I have read that over filling the trans can do this, or the fluid over heating. I am using the stock cooler threw the radiator. The transmission was rebuilt about 2 years ago and hasnt missed a beat or done this before. There are some climbs I have to go when I go out with my friends wheeling, maybe putting stress on the trans making it hot? I have also read that there is a thermo valve? that maybe be stuck or damaged? The trans shifts nice and has never given me a problem. The fluid doesnt smell burnt or discolored. I also disconnected the cooler lines at the trans to see if there was any blockage and noticed the fluid from one line was cold and one was warm, making me thing there is a blockage. Im thinking about an aftermarket cooler.. any ideas? Thanks!!