Car jerking while driving

What is your question?

I had a 97 Hyundai car that no one seem able to fix, I then ended up at a auto car sale and mechanic shop, they did not fix the problem either. They told me to buy one of their cars which I did, I purchase a 1999, VW Jetta with three months warranty, and from that time which was 5/19/2010 when ever the gear shift the car would jerk, the problem now it's jerking when driving especially when the speed is chaging or going up a hilL. The reverse gear is stalling too.