Help

My Duster is mostly stock. 340 with 509 Purple shaft Cam,Shaved heads,700 Edlebrock carb, Torker 340 intake,Headders,with a 4 speed and 391 posi. The problem is right now I run 245/60R14" and can spin them alot with little traction. I bought a pair of 15" Ralleys SBP at Mopar Fest and need some Ideas on what to use. Thanks for the reply!! Craig.