The data port is likely for the transmission. I tried to use a Scangauge with our '98, and it would only show voltage.
My thought is to use a non-contact thermometer to get readings near the sender, and compare them to your gauge.
If you really don't trust the gauge...
use an adapter to add a port, and install a go-no go switch and indicator light or buzzer.
or, just replace the sensor and gauge. $50 for a good gauge, $20 for a sensor, and a few bucks for 40 feet of wire!
1998 Monaco Windsor