Bob,
If it works at all, it's probably working as best it will. Lot's of 'lee-way' there, so making sure you don't exceed any of the ESC's current/voltage ratings is the first step. How hot does it get? Too hot to touch means over it's ratings. From there on, you're talking about having some sort of unusual test equipment/knowledge. Certainly not impossible, just not very economical or likely.
- 'Doc