The drive serve that comes off the back wall is a huge issue with folks trying to move up the ability ladder of racquetball. When serves come flying off the back wall the usual reasons are:
1. contact too high
2: swinging in a pendulum plane.
3. Twisty wristy syndrome (turning your wrist)
Here is a tip to fix these issues.
Get a mat and put it in the service zone. Then get on your knees on the mat and hit drive serves from your knees.
You should find it hard to do items 1-3. Now get to your feet and do the same swing minus the mat of course!
That should help fix the drive serve issue.