Recently had new engine put in

In November my 2000 Durango (Sport) suddenly seized the engine, and after much thought I decided to have the shop I towed to put In a new engine. I've taken excellent care of it and it only has 68,000 miles total. The only thing not working or in good condition was 3 of my electric windows. After I picked up the Durango from the shop I noticed that it doesn't have the power, kick in and the huge burst of power I used to get when you put your foot down on the accelerator, as to pass someone. Also my steering wheel has a lot of play in it, before it was solid and tight. there was no play. Also, a couple of times when I turned a tight turn my car shut completely off. And I also noticed when it was in 4WD that it didn't have the noticeable engage when I switched it over and didn't feel like it was grabbing or handling the same either. What would cause these problems? The automotive shop doesn't want to deal with me, and these issues were NOT pre-existing. I would NEVER have gone into debt $6200.00 if there were other issues. I have always loved my Durango for the safe, solid ride and feel I'd always had. I have owned this car exclusively for the last 14 years. Also, after the first 500 mile break in of the engine, would that make a difference in the amount of power? I would appreciate any ideas of what could cause these issues and how should I proceed with the automotive company? Is it fair to ask for diagnostic or to test computerized components? I'm just sick to my stomach every time I drive it now. It doesn't drive and handle the way it used to. What should I do? Thank you!