If I drained, my gears, transmission, and coolant... you think the car will run better? I already put Royal Purple 5W 30 in the motor with a gm filter, just the others I need to worry about. I was curious about this... thanks in advance

 

Possibly a little bit, but no sotp difference.
Synthetics are mainly added insurance for people that like to drive hard. Since it's a tad more slippery you'll probably pick up a few more hp, but not much.

 

i read in other threads that synthetic will make shifting a bit rougher for the t56, but i cant say from experience.

 

What about gear oil? Think I should change that? What does bad gear oil cause?

 

All oil is is a protective barrier between two parts moving against each other, which prevents wear and heat. Bad oil in the rear will just make things wear faster. Impurities can also cause problems. I would say get to it when you get the chance. The ring and pinion aren't too expensive, but the differential can get pricey. As long as you get the right weight 80W-90?, then you can't really go wrong, there's not a bunch of brand additives like in engine oil. Don't forget the additive for the LSD. I used that Trans-X stuff from Advance Auto- it lists the different automakers part #s lsd additives that it is compatible with, so no need to worry. I haven't had any problems with it. The stock 10 bolt likes to break by itself anyway, so no need to invest a lot in it.

 

http://www.royalpurple.com/prodsa/mgeara.html