Effects of trailer brakes and sway

So here's the deal: My trailer was loaded to 400 pounds below max weight. Tongue weight percentage was 12.3. I had just gotten the trailer back from a "repair" facility and was getting ready to head to the east coast. I happened to notice they had installed the axles backwards, rt vs lt, not up vs down. I drove back to the shop to have them reverse the axles (130 miles). They reversed the axles and I headed home. The trailer had minor sway which I thought was canyon winds. Also, the truck was working harder and gas mileage dropped from 8.9mpg to 5.8mpg. Also, two tires were running 45º hotter than the other two. Slowed to 35mph in a construction area on a 7º down grade. Upon exiting the construction doing 35, I proceeded to speed up due to the grade. The trailer then swayed dramatically and caused all 6 hanger brackets to bend, shifting the axles 2 inches to the left. The road was straight with no bumps. They are saying it's my fault. There are a lot of mistakes they made prior to this (which is why they installed new axles...backwards) that really isn't pertinent.