I have not heard of anyone installing a "shift kit" on a Crossfire transmission. Our automatic transmissions (NAG1) are controlled electronically. There are several companies that offer "tunes" . . . Eurocharged Performance is probably the best known (Eurocharged Performance Exotic / European Tuning Specialists) . . . They offer "tunes" (read as performance upgrades) for the ECU (engine control module) which also includes some changes to the transmission performance (shift points for example). Further they offer a separate upgrade "tunes" for the TCU (transmission control).

Shift kits are old school and pretty much not applicable to modern vehicles with electronic computer controls. In the old days, a shift kit would basically make the transmission shift "harder" (banging into the gear change) and effectively served primarily to shorten the life of the transmission. Stay away! Just sayin' . . . .