[pfreivald]

We've run mecanum on 9:1, 10.71:1, 12:1, and 12.75:1 reductions. Even at 9:1, the power draw started to get high enough to make us nervous (please don't ask for specifics--this was five years ago and I don't have that kind of memory!)

Our octocanum last year was 10.71:1 on the mecanum wheels and that worked exactly as well as we wanted it to.

So as others said: Gear it down. My suggestion would be a 2:1 (or slightly higher) reduction from what you've already got--either by buying new gearboxes (which will be expensive and probably require a redesign, if they're even in stock) or using belts/chain (which will be much cheaper and definitely require a redesign).