If you're running foams on carpet, swap the front one-way for a ball diff. I read somewhere that Tamiya dont make a front diff for the 415, but you can build one that works from Yokomo parts.
Go harder with your springs and oil, and stand the front shocks up. Throw on a hard swaybar on the front.
Otherwise have a look at the Tamiya threads here, you're better off asking in an existing thread rather than creating a new one. Also, do a search. Probably been asked before, too