I have a 2000 blazer s10 4x4. The transmission was slipping a little bit so i was told to change the tranny filter. so i did and the transmission worked great better than it did. then a couple of days later i was getting on the highway and i was getting up to speed. it was acting like it was in netural. there was no warning no noise nothing. so when i got it back i checked the fulid and it was where it needs to be. i put a little bit more fulid in it and it takes a little bit to get n gear but then when its at 30 mph it doesnt shift at all. i put a little bit more fulid in it and it works a little bit better but still takes forever to go in gear and there is a really bad transmission fulid burning smell. what could it be? do i need a new transmission?