I used to race a RC10GT back in the late 90's. Tuning was simple, and once you tuned it, you left it alone. Most of the RTR kits you can buy now are about as good as the old team kits. I would just recommend using a 3 needle carb. You really do have to clean it a lot though. One trick I used to do was wrap my servos and Rx inside balloons so the wouldn't be covered in fuel.
The electric stuff now though...they are just as fast, and much cleaner. If I got back into it, If probably go electric...only problem is, the technology with motors and batteries has changed so much on the last 15yrs, I have no idea what I'm looking at anymore... Which makes me reconsider nitro.