[AllenGregoryIV]

That's an interesting setup.
Going to 6 wheel dropped center will help but your current problem is that your drive train is geared way to high. Those look like CIMpleboxes when paired with the kit belts and pulleys don't provide enough of a reduction for the motors. (EDIT: on second glance those aren't the kit pulleys so you might be running 1:1 which is even faster)

I would recommend adding a center wheel that is about 3/16" lower than the current wheels and moving to sprockets and chain. 12 to 26 or 12 to 32 would probably be good. Though those are just guesses. You can use a design calculator to figure out your actual speeds; something around 8-12ft/s should be what you are aiming for with a 6 CIM drive. You would want to power the center wheel off of both of your gearboxes so that all three wheels will be linked and spinning at the same speed. That will also allow you to maintain all your driver train power to the ground even when some wheels are lifted off the ground.

AndyMark and VEX both sell sprockets and chain that would allow this fix for around $100.

Omni wheels will work but they cure the symptom not the cause of the problem.