I don't think it is a matter of backlash. I think it is more along the lines of incorrect pinion depth. In my opinion there is no ecuse in this if the person setting up the rear enhd knows what they are doing and has correct tools and takes the time to do it right. IT will not get better even if someone tells you it can. It can get worse though.
When setting up a ring and pinion it is important to get the correct pinion deopth and backlash with a good tooth contact pattern on both the drive side and the coast side on the gear set. I always put a hard load on them to resist rotation, making rotation to be difficult and require force to check contact patterns on both drive and on coast side of gears. The pattern I shoot for varies with gear materials and actual application.
I am pretty sure you can go to Randy's Ring and Pinion and see some charts pics and details and possibly troubleshooting onfo.
Ed
PS,
If using a spool on the street be sure you do not have Strange Engineering Race Axles in it. They will break uless the tires slip easily when turning hard corners. Moser. Mark Williams is ok.