Increase your reduction, significantly. With such a little reduction and 6" wheels, you're putting a large load on the motors, and they're drawing a lot of current to compensate. As a result, you're browning out your control system and/or tripping your 40A breakers (which may be the root cause of you describing your jaguars as "failing"). Additionally, with a large load on the motors, they will spin a slower rate (which is the root of the "CIMs supposedly draw less current at higher RPMs" comment).
I'd highly suggest taking a look at the CIM motor curves and reading some of the great material out there on designing a drive system for FRC.
http://www.usfirst.org/uploadedFiles...rves_Rev_A.pdf
http://www.chiefdelphi.com/media/papers/1378
http://www.chiefdelphi.com/media/papers/1443