Greg -
Fuel guages in boats are notorious for not working. And, if they do work, they read improperly. It's likely not the guage itself but the sending unit.
About 5 years ago, Bass & Walleye Boats Magazine did an article on how to rig the fitting for the sending unit in the tank so that it would work properly - at least some of the time! It would have been so much work to get to it on my Nitro 180 that I just decided to keep doin' it the lod fashioned way - check the fuel level by looking at the shadow on the side of the plastic tank!
Save yourself a lot of trouble, bux and frustration - just fill the tank to the top before every trip!
me!