My t-maxx 2.5 with a 3.3 only runs with the front wheels only no rear wheel drive. Could this be a blown rear diff?

it could be any of the driveshafts or the diff its ushally commonplace if a t maxx blows a diff out its ushally not the ring and pinion but ti could be we found that it stripps the spidergear pin inside the plastic spider gear case and you have to take it apart and clean it to find it REAL PAIN

It could just be blown bearings i would take the diff out and look at blown bearings or broken teeth, if its not making any sound when it runs (like a grinding noise) then your driveshafts could be stripped and its just spinning on the outdrive

Have you checked the drive pins in the rear center drive axle? If you lose either drive pin (shaft has 1 in front at trans and 1 in rear at diff), the shaft will just turn and not drive anything.

These need to be checked/tightened every once in a while - all of them, there are a dozen - 2 each on all 6 drive shafts.