[Matt Adams]

There's a few obvious double checks you need to do:

You need to use the spacers they give you to keep you gear aligned, they work well if you use them properly. Without them, the helical gears will be a nightmare. With proper spacers, you can assume almost zero losses. Ours out of the box were very fluid. If you need to make some, purchase a pair of digital calipers ($20 off eBay) and get them accurate relative to the gear box. Poorly meshed gears can make or break a drivetrain.

The other obvious gearing troubles:

Do you have your helical gears made such that you're slowing down through the gear box (as opposed to speeding up?) If this isn't the case, you may need too much current from your drill motors.

It'd be easiest if I had a picture of your robot, perhaps you could IM or email me so we can talk more. I'm extremely sympathetic to getting drivetrain issues resolved for student run teams, and am more than willing to talk you through some solutions.

Good luck!

Matt