The ACT shocks should be good for a couple thousand miles from the factory. I know that they ran them in their Iron Dog sleds (Usually rebuild in Nome) but didn't with the ACT shocks. Said they worked great for the whole 2200 mile race. And these guys are litterally beating the SH!+ out of there sleds for that distance. Your ZRT is much heavier than the 440's there running but they are carrying all the parts they figure they will tear off during a given section of the race. My 2000 Tcat shocks are still working good but only have about 1000 miles on them. If you've got the rear skid out have them rebuilt you won't regret the price you pay.