Then, continuing to include PSA testing with all your other bloodwork doesn’t cost you anything. I would keep doing it.

Consider that at 75y, your PSA isn’t high (just elevated). The Mayo Clinic recommends using age-based PSA reference ranges for PSA screening. Generally, the upper limit for PSA increases with age:
40-49 years: 2.5 ng/mL
50-59 years: 3.5 ng/mL
60-69 years: 4.5 ng/mL
70-79 years: 6.5 ng/mL

If you’re concerned about the rate of increase of your PSA, you should consider taking a look at your:
> PSA Doubling Time
> PSA Density
> % Free PSA

Also, consider other biomarker (genomic) and genetic (germline) test results.

If you’re still concerned, consider getting an MRI and see where that takes you. With all that information, you’ll have enough information to decide what to do next.