95 chevy lumina van apv

Hi, I am no expert but i think you might have 2 issues. 1. The fuel injector(s) is gone bad causing mis-firing and the jerks 2. The intake manifold is bad causing insufficient air to enter the engine causing jerks. 3. Or both of the above. Since it is happening at a certain speed my guess in fuel injector(s).I believe different fuel injectors come on a different speeds. The check engine code will tell the complete story. Autozone will pull the code from your car for free. Take the code and do some internet research before going to mechanic. Regards Ash