Questions!

[TranzAm98]

OK first off WTF. My drain plug for my oil pan is an 15mm not american, I know the cars are mostly manufactured in Canada, right?

T56 Tranny 6-Speed Manual
The other day I was out in my car and was going about 75 and went to shift from 4th gear to 5th gear and I accidently went from 4th to reverse at 75mph and dropped the clutch to engage which I thought I was in 5th. It made a very high pitch grinding noise when It went into reverse. I'm wanting to now change out all of the fluid in my tranny! The tranny and everything still shifts great and everything, reverse is still there, What do you think I should use for my tranny fluid!?!? I bought 4 quarts of Dexron III fluid and some Lucas hard shifting fluid to add to it! I have always used lucas in almost anything I use. Motor Oil, Tranny Oil, and Rear End Fluid.

What would be the best that you would recommend for a good rear end oil in my 98 Trans Am. Its a stock rear end and just want to add new rear end fluid. Are there any additives that are needed other than the rear end oil itself? I'm gonna but some Lucas gear lube in it also! Thanks and have a great week!

[Acceleration Junky]

You will find a lot of metric nuts and bolts on your vehicle. Your car is equipped with a reverse lockout solenoid that prevents you from being able to accidently shift into reverse after you are moving three or more mph. IMO, I would use dexron lll in your tranny and amsoil in your rear. I've seen some interesting things about Lucas additives enabeling foaming in gear oils. IMO, I wouldnt use it. But Im sure somebody can point out some positive aspects of lucas additives.

[CompSyn]

Check out this link for a comprehensive gear lube comparison -

GEAR LUBE COMPARATIVE TESTING LINK

CompSyn

[30thbird]

If you have a '98 as you info states, you have paper-lined blocker rings unless it has been rebuilt with something else. You should not only shy from anthing that is not certified Dexron III spec. but never use any kind of additive. The later carbon-line synchro rings ane a bit more durable to re-engineering the maufacturer's oil spec but not yours- stick to DexIII.
There is a reverse inhibitor on the T56 but no"lock out" . It provdes a high load to get into the reverse gate but it does not prevent it - as you have found. I suspect you did not actually get reverse and only got a clash. If you had actually gotten reverse the internalspeed of components of the trans would have made some serious vibration & noise. If you had released the clutch while actually in reverse, parts of you driveline would have been all over the road.