The Traxxas Titan 12T is a very weak motor. Virtually any other motor will work better. Even the Horizon Hobbies Dynamite 12T motor is better than the Traxxas Titan 12T. But if you want a really good brushed motor, go look at Holmes Hobbies.

Other than that, yes you can replace electronics with a different brand and it will work fine. The motor and servo sizes are all standard, and the ESC and receiver don't need to be standard sizes because you can stick them anywhere with foam tape.

The Traxxas 4Tec's limiting factor isn't its transmission, but its tire size. All touring cars have tiny tires that spin easily. You pretty much can't overload their transmissions unless you're using super-sticky tires on a perfectly-clean track, because they'll just spin their wheels if you mash the throttle.