Bot with treads has trouble turning

Bot has Tamiya Twin motor GearBox Set, L293D and 850 mAh LiPo. This battery:

It seems to go straight ok on the floor or carpet. Turning is a problem, particularly on carpet. If you slow a track down it tends to stall.

The gears seem kind of loose. Is slippage and jamming common? Is it underpowered for turning, particularly when there is good traction? Any ballpark ideas how long before needing a charge and is it okay to run it like 15 minutes straight?

Its the carpet, mine works well using 6volts through an l293 on tiles, its hopeless on most other surfaces - with more power like i have in mine it will shed its tracks on a grippy surface.

A solution might be to go with something like a half track skid steer, or just stay in the rooms with tiles.

Duane B