I am running 12.5's and I had to do a LOT of trimming. I would definately go with an 11.5 if possible. 13.5's would require TOO much trimming.
I already trimmed the back of front wheel wells more then I really wanted to and after this last weekends 4x4 trip I need to do more trimming.
2001 Ironman Daily Driver... 3.5" suspension lift (OME912 springs and 1" spring spacer), ball joint flip, 1.5" front diff. drop, 33"x12.5 TrXus MT, 16x10 Eagle Alloy rims, Interceptor, PV muffler, K&N air filter, Alpine Supercharger, Bilstein shocks, and some trimming.
2000 Ironman Project LS-1 VX... very slow progress but someday....... ohhhhh someday......