Dogg, are you sitting down? According to my diagnosis guide: "Noise in 1st gear & reverse," states that it is one of, or all of the above: 1. Oil pump system. 2. Input Gear Set. 3. Reaction Gear Set. Not good! We're talkin' about hard parts here.
You can do one of two things. Fix it before it breaks. Fix it when it breaks.
I like the SERTA trasnmission service GM uses. They give you a 36,000 mile warranty. The Trans is rebuilt, front to back. If you had your Trans repaired for the hard parts alone at an independent, I bet the difference would be about $400/500. Meaning....your rebuilt Trans would still have the old clutches, the same T-converter, the same valve body, and so on. With a SERTA, you get a freshly built Trans. I've installed enough to know that down the road, you'll be better off spending the exta $$ for a SERTA. Just my opinion.