2002 Chevy Malibu

I have a 2002 Malibu I recently had new catalytic converter put on the car, and I had the intake manifold leak fixed, which fixed the oil and fluid leak. However I am having the same problems as before which is. When I drive speed ranging 30-70 the tac goes crazy, the car shakes as if it's not getting car, the car stalls at lights and then cuts off. There is not check eginine light that comes on. Where could this possibly be comiing from?