I find it sad that a mechanics shop would not re program the trans for you. It's a private vehicle at this point so no chance of a school district coming down on them. I'd ask to sign whatever "release of liability" paperwork the mechanic could come up with and unleash that bad boy!
Wishful thinking... i know.
My poor 643 just can't muster a 5th or 6th gear no matter how hard I try. I'm jealous