2002 Dodge Caravan Shaking between 45 and 60 MPH

My van shakes between 45 and 60 MPH. Recently I had to have the entire rear end replaced due to a warped left rear axle and a messed up rear end. I have had the tires balanced, front end alignment checked good, and the entire front brakes (calipers, rotors, pads) replaced due to a frozen right front caliper. The tires and tread are also good. Had a full tune up done w/exception of cleaning the fuel injectors and the engine runs fine. The van shook before having the rear end replaced, and the shaking was the original problem I took the van to the dealer for. Is there anything I can check at home, or have someone else check without paying an extreme amount of money to have done that could possibly resolve the shaking?