Transmission Overflow, smoke, fire

I was driving along one day and looked back and saw a trail of smoke. Pulled over popped the hood there it was an oil fire. Without panicking I calmly blew it out (my baby wasnt going down without a fight). I noticed that the breather or whatever that thing is beside the part that checks the transmission fluid level had overflowed. That seemed strange as it had never happened before. I had just gotten over a 30 to 40 degree incline on a highway going about 70 or so when the problem occured. I restarterd had my gf rev it a few times while I looked inside the engine compartment and saw no more oil coming out. I grabbed some spare transmission fluid put some in cleaned everyting down with a paper towel ( I have the cleanest engine you will ever see) then hopped back in the truck. I then noticed that the 4wd high was on. I turned it back to 2wd and went along my merry way without any problem since. That was about 2 months ago. I just wrote it off as being caused by my driving on the highway in 4wd high without ant load and vouched to check the driving mode everytime I start driving. Has this ever happened to anyone and was I correct in my assumption.
I realised one thing I always knew, it is very important to keep your engine clean and grease free. Can you imagine what would have happened if I had grease all over my engine, my car would definately have been totalled. Since my engine was clean the only thing that could catch on fire was the transmission fluid that overflowed. I washed my engine myself with about 6 cans of engine degreaser, rinsed it off with some water, wiped everything with a clean rag then shined up the fan shroud, air intake, fuse box and other parts with armorall as soon as I bought my truck (no I am not Monk nor do I have OCD) . I keep my engine clean because if I am going out all dressed up and feel there is a problem I should not be afraid to pop the hood. If I dont know what the problem is and someone tries to help they wont have to be afraid to touch something and have dirty hands when they are finished. Also if you have a clean engine any oil seepage can be detected as soon as possible and you will know the exact location. Just a few words of advice when doing an engine wash, keep the vehicle running, keep water and degreaser away from areas where it will pool (like in the holes the spark plugs are located) and keep away from electrical fittings (a damp cloth will do well enough or a little degreaser on a rag). You never know a clean engine just might save your ride or your life as I am sure it saved mine.

Yes, our transfercases are not made for running at hwy speeds for an extended period of time. The transfer case overheat happenes quite easily. (Happend to me one time when my kid left it in 4hi and I didn't realize it). You probably shaved a little bit of life off the transfer case in the long run but it should be ok.