Start out with putting a set of wires ( fused ) from the battery, up the fender into the cab. Hook up a meter to the leads, and check the voltage when driving, to find out if you are over or under charging. This would be a good place to start with, rather then just replacing stuff without testing.
You made no mention of it, are the battery terminals clean and tight ? I would suspect so, with just replacing the battery. Did you check the other end for corrosion and tightness ? I am drawing a blank, but is there a fuse on the '00 just behind the battery on the firewall for the alternator circuit ? My '01 has only been gone for about a month, and the layout is quickly disapearing from my memory...
If it is where I think it is, is the fuse fully seated, and the contacts clean ?
The reason for the clean/tight questions, is it could be adding resistance to the circuit, and the battery might not be getting the full charge output from the alternator, and maybe causing the batt light ?? Just guessing, until we get a bit more info.