Marc,
my '02 standard ZR, I was at best getting 200 miles before the rear shocks went south. Had them rebuilt a few times and also replaced with new. One good hit and the rear suspension would start riding harsh. Would not come back the next day. Rebuild or replace the shocks and it would be fine again for a short time. When right, the sled rode fantastic. Some say stiffer springs cures problem, less continual shock movement. I am currently having an M-10 installed, will give a report when I try it.
mike