Help with E Maxx with MM esc and 5700kv motor

[offroader]

Hi guys, this is my first crack at a Brushless conversion I'm running a stock E maxx with a single motor 5700kv CC motor and MM esc using a external UBEC and a 2100mah Thunder Power Lipo. When I the bench this everything seems fine with lots of power. I did my first test run today on grass the motor has alot of power it was doing wheelies off the start I ran the truck for about 10 mins and noticed the battery become weak ( I was lucky to when the battery cooled down the swelling went down and I didn't destroy the battery). When I checked the Lipo pack was too hot to touch and swelling the ESC temp was about 120 F and the motor was about 100 F.
My question are:
Is my setup too small, battery, motor or esc?
My gearing was 18 pinion and 66 spur gear is this not matched right?
What if I put to Lipo's in parallel would this help the battery to run cooler?
Thanks for any help on this matter.