On my 97 T-bird sport(which weighs about 3990 lbs), I still have the oem Motorcraft/Ford "sport" shocks (coil-over shocks, NOT struts), and they have 105k miles on them. The ride still feels fine, and I still haven't "felt" any need to change them. Those sports shocks are stiffer than the regular T-Bird shocks, so the car rides pretty stiff anyway.
I also have no idea when They "should" be changed...From what I've heard the oem T-bird shocks are very durable.
I also have no idea when They "should" be changed...From what I've heard the oem T-bird shocks are very durable.