Does anyone know what the life span is on the expensive self adjusting rear shocks on a 2001 Yukon 2WD. I put new tires on and the ride is bouncy on rough freeways. New shocks in the front because one of them was squeaking. I had put on Bridgestone Alenzas first but the ride was like a buckboard so I swapped them for Michelin Cross Terrains. It still bucks even with the softer tires. There are no leaks on the rear shocks but I wonder if they may be causing the bad ride.