^^ What Bill says ^^
Additionally, I've found limiting STG end points considerably for speed runs and adjusting STG expo for softer action at beginning of the steering wheel helps. You don't want a lot of quick or full steering action at speed. Normally set my STG end point using the least...
Those are the two surfaces my Rustler runs. On-road and grass. Grass is pretty forgiving if like a baseball outfield or soccer field. You can run pretty close to an on-road set-up on it. Field grass not so much so.
Sounds like you have a plan. Making changes one or at most two at a time...
Hey, DavidB. Post up a picture of the slash in running attitude if you have one. That will help us help you. What surface are you running on? Multi-surface or dedicated surface?
Are you running a rear spoiler? Cutting it down or eliminating it entirely may help. Adding weight to the front...