2001 Dodge Caravan Bottoming Out of Rear

I just recently had new shocks installed front and rear. They used Monroe replacement shocks, which appear to meet Dodge original specs.

However, after I picked up car, it seems as though the rear bottoms out when I go over a bump and/or over a swale in the road. There is large bump in rear and it seems that the cab drops to the frame.

I've returned the car to repair shop once and have to take it back again. I did not have this problem before new shocks were installed.