I want to add an oil pressure and water temp gauge on the passenger side. Does anyone know if they need their own sender or if I can piggyback off the existing sender? My gut is telling me I can't piggyback because having two gauges hooked to one sender will screw up the ohms from the sender and cause the gauges to read low.

If I can't piggyback I will probably go mechanical.

Depends on the sender you have now, if not all you need is a dual sender. (like you would have on a fly-bridge boat with two helm stations.)