I saved the game with seven blue containers of gasoline, a couple of beer kegs and some jerry cans, all full of gasoline. When I loaded the game the truck was bouncing all over the place and crashing into things until it finally flipped over on its side, after which the bouncing stopped. When I turned it back upright it continued bouncing again.
I tried reloading the save but it didn't do anything; it was still bouncing. I let it bounce around until it flipped over again, and entered the back and tried removing some items, starting with the blue containers. I took four of them out and then flipped the truck upright again. This time the bouncing didn't seem as bad as it was before but it was still pretty bouncy.
I went back inside looked at one of the kegs and instead of moving it I used the grab function because it is smaller and harder to keep the aim point on the item with the bouncing while waiting for the move timer, which is faster. Immediately the bouncing stopped.
Maybe the problem is the kegs. So I reloaded the game to see if I did something different what would happen. Reloaded, entered flipped over truck. Instead of moving the blue containers first, I grabbed the keg. Game crashed. Reloaded. This time grabbed the other keg. Game crashed again. Then I tried using the Move function instead of Grab and it again crashed as soon as I hit the E key to start the move timer.
This time I tried replicating what I did first. I started by removing one blue container, then the keg. Crash. Next time two, then the keg. Crash. I kept increasing the number of moved containers, and when it got to four that seemed to be the magic number where I was able to grab the keg without the game crashing. That was also the point where the truck was bouncing less.
I supposed the fix could be just putting the kegs in the container storage instead of placing them in the back. I don't know why I did that in the first place except that I just liked the look of them all in the back.