Need help with E-LST2 gearing...

I'm still messing with my LST... It's got an 2-Speed. The motor (Plettenberg Bigmaxximum) stays cool like a fridge. But my ESC (Quark Airmaster 125B with externel BEC) gets hot like fire after 10 minutes... :( I'm running stock gears, so 18/70 and 25/63. And last time I mainly ran in 1st gear, so why does my ESC get so damn hot? :S

Sorry for the off-topic a bit, but this will maybe also help you to decide for a good gearing. The Bigmaxx has 2300kv, so its like a Mamba 2200kv...