IMO, first and formost on determining what kind of truck it is depends on the axles, then the tranny and lastly the chassis.
I think the axles say the most about the rig. Is it a TXT, a Clod, a TLT, Axial, etc. Then the tranny makes a difference. For a Clod, built into the axles, it does double duty, thereby sealing the Clod name. For a TXT, you can use stock, which would seal the TXT name or you can use something else, which would push more towards custom. On TLTs, most of the time the tranny is from something else, stampede, axial, RC4WD, etc, which pushes it more towards custom. Axial can go either way. If you have the stock tranny then your running an Axial. If something else, then custom.
Chassis plays the final role in this. For Axial rigs, the stock chassis or custom one doesn't matter too much if you are using Axial axles and tranny. For TLT, the chassis doesn't matter much. But on Clod and TXT, where chassis have very specific names, it makes a difference. On these two the chassis name actually gets put into the name of the rig. example: Clodzilla or TTR TXT, etc
Just my two cents.