...for your electric, you can pick up a 4200 or 4600 pack that would give a LOT more run time w/o having to even change gearing (Probably 4-5 minutes minimum)
You may drop a tooth or two on the pinion gear and get even more run time if that's what you are looking for.
There are some LIPO options for batteries as well, but you'd probably need a NEW charger too (depending on what you already have)