what makes my car jerk when i get to 50 mph?
Could be a lot of different things. Could you elaborate more on the issue at hand, and also on the vehicle? Mileage and maintenance history will help, but above all, we need to know as much as you can tell us about the issue. This description would be okay if we were about to take the vehicle for a test drive (and even then more details would be appreciated), but we can’t do that over the Internet.
I Have alot of miles on it and there is a bad caliper on the left front. also i had the transmission rebuild, and the 4 wheel drive dont work all the time.
If that was your idea of elaborating on it to give people more info then no one here will be able to help you.
Define “a lot of miles” When was the last time the plugs, air filter, and fuel filter were changed?
The torque converter lockup engages on my 2000 S10 Blazer between 40 and 50mph. Did this start after the transmission rebuild? What is the charge on the battery? A battery at 25% charge (12.1V) will cause drive-ability issues, i.e. torque converter will not engage and idle is a few hundred rpm higher on my Blazer.