I have a 2000 Montero sport. I have always had a problem shifting into 3rd and especially 4th when we would take out the battery. Then I took it to my buddies house and we replaced the oil and such. We put everything back on and the whole nine yards. I went to back out and it wouldn't actually move until it reved to 4000 rpm (its an automatic btw) so I backed it out of the garage and didn't think much of it. I went to leave his house later that night and I put it into drive and it went to 3500 rpm and finally stuttered a couple of feet and went back to idle speed. It did this a couple times and fixed itself. I get down the road fine then I stopped and turned onto the highway I was accelerating and it was fine up intill shifting into 4th. It went to about 5k rpm and it didn't shift so I let off the gas and then it just covered the road in white smoke. It looked as if a cloud just came down to the ground. it looked pretty cool but it now smokes whenever I put it into drive and step I'm the gas. The car won't even move now. If anyone know what may be wrong it would help a lot. It would be a waste to rebuild the tranny because it would cost more to rebuild it then its worth.

 

How many miles....? What grade oil did you use...?
Sounds like there was an existing transmission issue before, now you have a motor problem.