Van starts shuddering when I Accelerate , has low power. Idles fine. Shudders until it shifts into passing gear, runs smooth until it drops into driving gear and then starts shuddering again. What could the problem be?
Generally has to do with the torque converter and or other internal parts sticking. Not using the manufacturers recommended transmission fluid may also cause this situation. If this started just after a transmission fluid change they may have used the wrong fluid.
What I would do first would be to have the transmission fluid flushed and filter changed. Then I would add in some “Shudder Fixx”. All you have to do is add it to the existing transmission fluid. Yes, I have done this before with great success.