Black Bart's in Flagstaff is one of those parks that has over 100 PSI all the time and announce it several places so RV'ers won't miss it. I was there a week ago and tested my pressure gauge. Worked great, right at the 110 the told me they were running. So I'm pretty confident that the pressure here at this park is the 104 PSI that I'm measuring (Sioux Falls).
I plan on running the test proposed earlier by replacing my brass pressure regulator with an adjustable one from Amazon. Should have it by Tuesday and I'll report back.
I can't run the test here at 104 PSI because the bathroom sink valve drips when the pressure is over 70 PSI and I don't want to temp fate and have something blow out. The new pressure regulator (always wanted an adjustable regulator - this is a good excuse as any to get one) should show me if it's just a bad reducer or if I need to dig deeper into the plumbing.