1995 Plymouth Voyager Speedometer and Tranny Problem

I've just had my transmission rebuilt and it everything worked o.K. Until about two weeks ago. My speedometer started going on the fritz first, jumping from 20 to 85 when I think I'm doing 40. After about a week, the speedometer was getting worse and when it would "max" out at 110, the whole front end of my van would jerk and sound like it was gonna stall and then accelerate again. It happens so fast that I can't tell what's stalling. I need help figuring this out because this van is all I have and can't afford anything else right now. I've had the transmission rebuilt a total of three times, just in case that matters. This is also the second transmission this van has had. Please help me! Thanks!