I would recommend the GM cooling system pellets. They're only 4 bucks or so at the dealership. That way, you know you're getting the right stuff. Bars Leaks is supposed to have the same thing, but only one of their products. Some of the BL stuff is much different. I dunno -- I just use the GM stuff because I know it's right. Just drain the system and refill with the pellets -- no need for any flushes.
As for the tranny, it's just Dexron-3 as far as I know. Check your manual to be sure. Get a filter/gasket kit at either the dealer or your local retailer. Aftermarket should be fine here. They're usually cork gaskets -- I've used those many times before with good results.
Good luck, and don't get too messy!
