Well the big tires are just too much for the 370 (the biggest of the 3 stock motors) even with the ultra low aftermarket transfer case and gear reduction box. Some of that can be attributed to the all metal conversion (this thing weighs more than some 10th scale RCs) and I haven't even added lead shot to the tires yet. So desperate times call for desperate measures..
More than 10yrs ago I got acquainted with brushless motor systems and they were EXPENSIVE! I bought a Castle Mamba Max for my Traxxas Stampede and it was somewhere in the neighborhood of $350 if I remember correctly. Well the Chinese are selling them now at ridiculously low prices. I came across a 7800kv 540 with a 120amp ESC for under $50! So I purchased a RacerStar 2430 sensorless waterproof 4 pole 5800kv motor (60,000rpm!) with a 25amp ESC for $28 that can run 2s or 3s lipo packs (they claim).
Now I know for a single speed crawler you should run a sensored 2700 to 3300kv motor for lots of torque and no clogging on take off, but.. If you've got a 2 speed transmission ready to be installed (which I do) you can get away with a higher kv motor. Now the clogging is unavoidable with a sensorless motor and the Chinese haven't gotten in the sensored market yet, but it's negative effects can be reduced with a tiny (8 tooth) pinion gear. So here soon I'll be doing donuts and wheelies in high range and crawling like a beast in low range.
I also had to order some T-plug connectors for my lipo packs.