Take your truck and run it across the ground and lift the truck up.. all the wheels should keep spinning freely.

Frying your bearings from what i've found is this.

1. Mesh is to tight
2. clutch not shimmed right
3. warped clutch bell
4. To much play in the whole clutch bell/assembly
5. Bad shoes to much slip cause major heat
6. using cheap bearings
7. To much chassi flex

I've had bearings last 1 tank to 3 gallons,

I think it comes down to your clutch, I like to stay away from carbon shoes.. they seem to kill my bearings the fastest