Shell vpower 93 should be available.If I recall correctly it is 91 octane. You dont need 93 at at 4200 ft which is the elevation of Salt Lake City.
I haven't found any place in SLC that sells 93. But the 91 generally doesn't have ethanol in it either.
My recommendation is to get the best quality fuel you can find - Chevron, Shell, Texaco around here - and see how it runs. My car is tuned near the edge at 93, so when I'm in UT I keep aware of possible knock.
If necessary, buy some good octane booster if you are forced induction.
The air there is hot and dry, so lots of O2 that is just waiting to detonate.