unfortunately Ryan its probably the high centre of gravity due to the ABS shell.
A lexan shell weighs virtually nothing so does not adversely effect the cars handling/grip under braking/ cornering etc... whilst the ABS is probably close to 250grams (approx 25% of total weight). Bear in mind the type of shell, your Cab style is not used in any "full size" racing so I'd guess that aerodynamics and shell weight distirbution is not best for suited circuit racing more akin to banger racing.
You could change the front and rear springs (medium all round) and make sure your running 50 shore fronts and 42 shore rears.
But setting up a mardave is definately 90% tyres that suit your driving style. I like mine to slide with minimum grip as I use the motor to power the back end around turns.
Good luck trying all the various combinations, it took me 2 years to reach the setup I have....
