I find it hard to give any advice on your
oil question. U did not give any info on the engine? What is the engine FE,Windsor? Is this a race engine? When u say "crusing at 90 or 100" what rpms are u turning? Please give more information.
Is the Powermaster ALt. a Single wire? If so it my not be grounding well. Add a ground strap. Solve this first then see if your
oil temp gage is in error. Plug in mechanical
oil temp gage and see what the temp reads.