Manuals weren't available after the '94 interior make over. It's when the hardcore sucking of GM began. The seats, while much nicer than the '97 & up GPs, were not nearly as comfy as the AQ9 seats available in the pre-'94 style interior, the DIC was reduced to a much smaller, much more simplified version of its predecessor (no car outline), the available hood louvers were made shorter, etc.
Anyway, really the only thing I'd look into/would be worth doing is to upgrade to either a 2000 & up 3100, or any 3400 top end. Better yet, 3500 top end swap.

Much more involved (OBDII swap, fly by wire throttle, etc), more expensive, but it will net you much better numbers. The 3100/3400 swap will only get you another 15 - 20 horses at the crank. The 3500 will be anywhere from a 30 - 40 hp increase, depending on the year and car.
Otherwise, it's basic things like an FFP underdrive pulley and motor mounts (which you'll have to find used, since they no longer make them), exhaust, etc. Headers aren't available for the 60° V6s, and due to them being an OBD 1.5, you can't even get a chip for the '94 - '95 GPs.
BTW, if you don't have it already, every '94 - '96 GP came prewired for HUD and DIC, though the DIC MUST be out of either a '94, or a '95 (again, on account of them being OBD 1.5).