Yes, gear and pinion too tight. Helis often have a slots for screw holes that let you slide the motor to adjust the mesh, but I just looked at my esky lama (same as Comanche, just a different body) and it doesn't look like it's adjustable.

Ya, the extreme motors will be more difficult to turn because they use stronger magnets.

I don't think I've ever bought a bad battery. I had one that never performed very well but that might have been my fault.

You say the stock motors couldn't lift the heli. You mean they couldn't from the beginning or that they wore out after a while?