Make sure to take a good look at the magnet, if the magnet is easy to see and had distinct ridges on the top, it's doing just fine. If it is a massive lump of black, and there is no clear shape to the magnet, you might want to look at the fluid more closely, try to find anything that looks like metal shavings. If you don't find any, that's a good sign.
Might also want to take the time to put a shift kit in, 40 bucks on Amazon, it will help keep the transmission running longer, and prevent future problems.
It's really quite simple, follow this link:
http://www.grandprixforums.net/thre...ransGo-Shift-Kit-4T65E-Very-Detailed-Pictures
You will notice a big difference in the shifts after the kit, and the extra springs and spacers will actually save your trans from more wear by decreasing the time it takes to complete a shift, and allowing the clutch packs to slip much less than stock, preventing them from wearing down or overheating.
A large flat tote is useful to catch all of the trans fluid, less cleanup afterwards.
If you do the shift kit, grab a scotch brite pad. Not necessarily needed, but recommended.
Lastly, use the right fluid. AcDelco Dextron III or Dextron VI is the best, but usually the most expensive, it's what the factory fluid is. Most brands will work, as long as it is a Dextron III or Dextron VI specific fluid.
Oh, and be careful when pulling the filter out, try not to break the tube off inside the trans. If it happens, vise grips work. The seal will be a royal b1tch to get out, but be gentle with it. If you scratch the inside surface of where the seal fits into, it won't seal properly. And you can re use the factory ribbed steel and rubber gasket, just check for cracks or splits on both sides.
I think that's it. Good luck.
Edit: yes I know I type slow...