Do you have an electrical or mechanical gauge? If electric, just like Jake said, perhaps your sending unit craped out, if there is an open in the wire the gauge will max out. I also read that you have a ten quart pan and you put ten quarts of oil in with an additional quart of Slick 50, I think you are a tad over full, but this is not the cause of your high pressure reading. Normal cold thick oil pressure at idle can be 70-80psi until the oil thins out with heat.