How many springs are installed on the trem? Some people use 2, but I've found that doesn't give enough overall tension. It's enough to hold the trem level, but not enough tension to keep it going back to a neutral position after doing a bomb dive.....If you have 2 springs, try adding a 3rd, and if you already have 3, try adding a 4th. It'll take some time to adjust the springs to get the correct tension. Don't know if this will help, but it's worth a try.....

Oh, and be sure all the hex nuts are tight at each individual saddle....