Lukewarm water from water heater

[Jayne-O]

Hi Everyone. Hey our 2017 305RL water heater only heats to lukewarm. It used to heat much hotter to the point that I'd have to hurry and mix cold with it. That hot. But now it only goes to a lukewarm such that you wonder if you want to shower in it. I did a number of tests: after I had drained my hot water heater, rehooked up city water, flushed lines. I first put the electric heater on for 1.25 hours. Lukewarm. (I ran the faucets for quite awhile to drain some off.) Then ran electric and gas heater. After an hour, lukewarm. Drained off a bunch more water. Gas kicks back on (with electric still on), still lukewarm. Does it sound as if my thermostat is giving out? Can I still use the water heater with both gas and electric so I at least have non-cold water? Safe? Thank you.

P.S. I did read the files available here, but none helped for my situation.