RE: REPLACE STOCK RADIATOR OR NOT?
I would go with the 180 degree Jet TStat, the CAI (your choice of brand), and the DiabloSport Predator for tuning. Those are probably your best mods - dollar for dollar.
The 6 speed has a very good flowing stock exhaust, so unless you HAVE to have more sound, and a few more ponies, keep the stock system.
As for a radiator - never hear of replacing the stock one. Change the thermostat to the Jet 180 and there should be no need for an expensive radiator replacement.
After that, you're into heads, cam, intake, OR forced induction. And THAT'S a whole lot more money.
Good luck.