Wellllll, I got the car back from the tuners, it passed SMOG and everything!! I did two big driveline improvements: T56 rebuilt with stronger paarts and OEM 3.73s (new bearings, etc as well in the rear-end). I babied the car for about 1000 miles, which was over-cautious, but somebody has to be right? Well, here are my observations/thoughts on the swap:
1) A little gear noise, but only under 1500 rpms and typically only in 6th, sometimes 5th gear. Easily tolerable, and not noticeable at all with loud music or T-tops off.
2) Despite what some people with 4.10s say, i notice a decent difference in acceleration, first gear is still usable, but more than able to break loose my balding F1 GS-D3s. Now given, I went from 3.42s to 3.73s, so people who have ever driven a car with 4.10s will tell you there's no difference. I havent driven a 4.10 M6, so I DO feel a difference.
3) With the 3.42s, my speedometer was near perfect until 85mph. Now my speedometer is about 3mph off (on the fast side) after 65mph. So: at 75mph, im really only doing 72mph. RPMs are a little higher: Im at 2000rpm at 75 ("78") mph, instead of 80mph.
4) Mileage....I havent lost any MPG.... I believe the reason for this is that the car was finally tuned for the first time. SO... whatever MPG i might have gained from the tune, i lost with the gears. I have a plan to get some MPG back though, in the form of QTP headers sitting in the garage, as well as an LS6 intake and another tune by the end of september.
Conclusion: I chose 3.73s over 4.10s, and I love the gears. I would reccomend 3.73s to anyone who has an M6 DD and wants some more Seat-of-the-pants feeling.
__________________ NEW!!! 1998 NBM TA M6, BONE STOCK!
**SOLD** but not forgotten
1998 Trans Am M6:
CheatR cam, 3.73's, lid, LS6 MAF, ASP pulley.
post-dyno: LS6 intake, p/p TB.