I assume the 3450kv is a 550 size motor and you'll be running it on 3s? If so it can be geared to love but isn't going to be too fast. I'd get a 4074 size motor on 4s instead so temps won't ever be a problem.

If your truck is a 4910 with the stock drivetrain you are going to have problems no matter which motor you choose. I knew someone with a 550 motor on 3s and the plastic driveshafts kept twisting all the time. I shimmed the older style diffs for him after he blew one up and they seemed to hold after that. The black trans was another story, the single speed conversion and other gears weren't up to the task. We had to do the mod where you put 2 gears on the intermediate and output shaft instead of only having one on each. Combined with a metal geared input shaft the transmission was then able to hold up to the power.