Bill,
I too have the unlimited prepay grandfathered plan. I don't know if you are having the same experience as I, but, Verizon seems to be more aggressive at slowing this service down than they have in the past. I have gone to many of the same places that I would normally get 20-30mbps down that now I am doing good to get 2 or 3 in the exact same spot, at the same times of the day.