[Ian]

What kind of panhard bar are you running? the panhard is the lateral locating device for the rear axle so if its bent (i have no idea how that could happen, but anything is possible) the rear is going to be off. Usually when the suspension doenst travel enough, that means the shocks are busted. I'd check them to see if they're leaking oil at all. My guess is that one or both of your rear shocks is broken or the rod is bent.

This is gonna sound off topic, but its not. How do you trailer your car to the track? Where do you hold it down? if you hold it down from the rear, the shocks are going to be moving the entire ride to the track and that heats them up a good bit. Eventually it could lead to shock failure. Just a little FYI for you.