My ESC is too hot?

The ESC in my converted hyper 7 is running too hot. Over the winter this set up has worked well, but the outside temps have warmed a little and they are sure to go up a lot more.

I have a BK 12020, Ubec, 7xl, all on a single 4s lipo (Kokam 3200). 12t pinion, 51 tooth spur. The ESC and wires are all getting very hot (I don't remember what the temp was). It even shut down on me and went into full speed reverse. Crazy! The battery is also getting too hot (160*). I think I will reconfigure my setup to use two 4s packs. That should help in the battery department.

The biggest problem is finding a smaller pinion to try. Mike is out 10t pinions.
Am I headed the right direction try to find a smaller pinion? Would it be hard to take a 4 mm pinion and bore it out to 5mm. Is there anywhere else to find pinions? Thanks in advance.