Hmm... if one of the 99-00 guys doesnt reply here shortly, Ill check the design of the dash in your truck. Im *pretty* sure its very similar to my 2003. In my 03 there is a giant trim piece that surronds the gauge cluster, radio, climate controls, steering wheel and light controls. This ENTIRE piece just pops right off with a little pressure. Once that piece is off, the radio is just held in by a few philips screws. Once in there, you can get to the connections behind the radio. There you should be able to see the split or interconnect for the TV/VCP modulator. Luckily, dash access in the GM trucks is very easy.
Btw... before you take apart the dash, make sure there isnt some sort of master power switch for the VCP setup. It sounds to me like what is happening is that the modulator is stuck in the transmit position which severely distorts every other FM channel, as used to happen when I had the CD changer on in my Continental.
Good luck!
Ian.
