I have a 2001 hyundai sonata with a little under 150,000 miles on it. I have owned the car for about 3 years now and I do not know how well the previous owner took care of the car, but I do try to keep up on the 'preventative' maintenance. Anyhow, recently I was driving down the road, and the car jerked like it may have slipped out of gear (it is an auto transmission), but after it did that, when I came to a complete stop, the car didn't roll forward like it usually does. I drove it home (thankfully I didn't have far to go), I let it sit for a while, checked the fluids, and everything was normal. Then I took it for a test drive around the block and it worked fine. I didn't think anything more about it, until it did it again around the beginning of this week. I ran the gas out of it and put some fuel system cleaner in it, and then filled the tank, like I was supposed to. Well, it did it again. I am starting to think that this problem is a transmission problem and not a fuel problem, but I was wondering if anyone else had the same or similar problem and what they did to fix it? I don't want to continue to drive my car if Im going to end up having to rebuild the whole front end of the car! Thank you so very much for sitting through my long winded question :)

Every 30,000 miles, drop and clean the transmission pan, change the filter, and refill with ATF. If it hasn't been done recently, I would get it done right away. Should the problem persist, the transmission likely needs rebuilding.