What is a good additive to extend the life of this transmission?
Nothing. If it's working right, no additive is needed, or they would have spec'd it from the factory. There are various products out there to stop leaks (softens seals up) but it didn't come with an additive from the factory, and I've yet to see it recommended by GM.
Yep, I agree with Tony. Substitue a quart of tranny fluid with Lucas and use the high mileage tranny fluid. I've owned a '99 Tahoe for the last ten years with 230,xxx and I srvc my tranny(just the pan) along with all other fluids, every two years. No metal flakes, slippage, or skips and it STILL runs and drives damn near better than a 2012!. There's nothing like them Chevy 350's and I hate that they quit producing them. Good luck on your decision and continue to take of that Chevy so it can take care of you! :-)
