The tmaxx never really did turn great, by design. The key reason is the 4wd drivetrain, more than bump-steer. The only way you can really minimize this is to place shims between the steering rod and steering knuckle by the tires. One #4 washer each ought to do the trick.
My guess is you, or someone else before you (if its used) put the turnbuckles on the wrong side of the steering arm. I believe they go on the top (the side facing the chassis), and the bottom on the knuckle side. Mine did that after I tore it down, and finally fixed it with that.