I have the opposite problem (sort of). I did double check the ohm reading. My new sending unit is rated at 30 ohms and the new 12v gauge I bought is also rated at 30 ohms. When I fill up the needle buries all the way to the right past the full mark. It goes at least 1/4 to half a tank distance past the full mark. The strange thing is that once my fuel level gets down to about 3/4 of a tank the needle is reading close to the 3/4 mark. When I am sitting on 1/4 tank it is darn close to right. I test this theory by checking how many gallons it takes to fill the tank. Based on the capacity listed in the owners manual the amount of fuel needed to fill the tank is very close to what you would expect sitting at a 1/4 tank on the gauge. This is a gremlin I just live with because on the low end I know it is close to accurate.

Dave from Northern Kentucky
My 54 3100