Ive got a 96 4wd blazer with a 4.3l vortec. It has been fine until one day I noticed smoke under the hood, and it looks like transmission fluid has been coming up through the fill tube. It ran low on fluid for a couple days until it stopped shifting into third, when I replaced the fluid I still had the problem.

It will grab 1st and 2nd no problem, but when it gets to the point where it should shift to 3rd it will slip and rev, that's it. I did notice that if I rev it to 5,000rpm as soon as I take my foot off the gas it will jump into third, but I can't do that for 4th.

any ideas?