I have a 96 as well, the graphite looking stuff is Torque Converter material. It is normal to have a little coating in the bottom of the trans pan, an excessive amount IS NOT GOOD. There is several things that could cause the large amount of material that you are seeing. One would be Hard acceleration with a bombed truck on a stock trans. You don't have your truck profile filled out so I don't know if your bone stock or heavily modified. The bottom line here is you might want to start saving for a new trans. You could go with DTT or ATS but that's a disscussion for a differant day.
I am currently in the same boat your in. I am mildly modified and drive like a grandma trying to milk every last mile out of my trans. Your on the right track with the trans guage, just keep on the trans services and make sure the trans doen't heat up and you should be able to nurse it for a while. I wish you the best of luck. I am sure some one else will chime in here and give you more info. I hope this helps. . Oh ya you might want to think about getting a MagHytech Double Deep pan. It hold more trans fuild and keeps trans cooler longer. any way Take care and good luck. .
Greg