120 volt hot water tank

I kept mine at 145 deg F. that worked out well. However it might be the arrangement of capacity rather than just the setting. How old is the heater? If it's more than 10-12 yrs, the element could be almost done with it's lifetime.

20 gal tank 2 months old.

Have you tried yet raising to 145 deg F and see if that helped? How many people are using your hot water in your household?

If you have questions, why not speak to the plumber/installer or repair person?