I would say that a new mill would be a good idea, but if you dont have the money to upgrade, make due with what you have. As soon as you get more power, other things are going to break. I would upgrade other things before the engine, to ensure durability with the new engine. As soon as you go faster, you break faster (learned that the hard way). I have found the stock turnbuckles to be a weak point. Titanium turnbuckles are a good way to go (Lundsford makes a good set). Also, i would go with some RPM ball cups on those turn buckles. If possible, get some RPM a-arms all around with a rear RPM bulkhead. The only other thing i can think that you might need is CVDs. They make the truck a lot smoother and they dont fly out and get lost like those damned dog bones. Now, if you dont have money for all of that, replace as you break the stuff... Oh, i forgot to mention... FAILSAFE!!!
Good luck man. Welcome to RCNT. PM me if you need anymore help. I know rc10gt's pretty well.