I agree that this sounds like it is hitting the current limit on the Jaguars, and that the automatic voltage ramp will likely work. VexPro Jaguars (and TI jaguars that have been upgraded with the v107 firmware) have a higher current limit. Is it possible that the working jaguars have the new firmware and the non-working one has older firmware? See
http://www.vexrobotics.com/vexpro/mo.../217-3367.html