Temperature Gauge Problem T210

I'm driving a 1986 T210R.

400 hours ago we had a reman engine installed and ever since the CHT and
oil temperature gauges(original) haver read higher than they used to.

Over the last couple months the temps have been climbing until now the
oil is above redline and the CHT near redline in cruise. We have an
engine monitor with all EGT/CHT probes and it says the CHT's are fine,
hottest(#1) is 370, lowest 315. We don;t have a secondary oil temp
gauge but the oil pressure is running 58-60 steady as a rock no matter
what the oil temp gauge reads.

The high temps displayed on the old gauges will change if the electrical
load is changed. Higher the load, higher the temps. With everything off
but the master switch, the displayed temps are close to normal but still
a tad high. I'd say the oil temp varies 50 degrees between no load and
say a 60 amp load. I tested with a digital volt meter and the voltage
stays in a range of 27.6 to 28 vdc no matter what the load is.

There are 2 alternators, a 65 amp and a 90 amp, both functional, temp
display does not change if running on both or either one. With both off
the temps drop even more, but the voltage also drops to 24.5-25 volts.
Not sure if the additional drop in temp display is because the voltage
is so low?

Anybody have a clue as to what is going on? We are stumped as is our A&P.

thanks, Scott