Shaun.. it may sound stupid, but I would simply dissect the suspension piece by piece and see where the hang-ups are.. Start with the shocks.. remove them and move them through their range of motion.. make sure they are smooth and linear. Then move to the rocker arms. remove the suspension push rod and move the rockers through their range of motion.. Aagin, feel for anything binding or hanging up and address. Next, move each wheel through it's range of motion.. You are now only really looking for a bent pin or something similar.. Again, address as required... Finally, turn the front steering knuckles, and check as well.

If it were mine, I'd strip it naked and clean the daylights out of everything.. never hurts as good maintenance...

If it's binding, then 'something' isn't working right.. could be almost anything...

There was an interesting story in one of the RC car mags this month.. it had to do with ensuring full range of steering and lack of binding through the entire range of motion of the suspension, not just ride height.. So turn everything your can at all the extreme's of suspension travel...