My experience with an aftermarket sending unit was pretty bad, too. Take a GOOD look at the quality of the windings on the rheostat on the old and new unit - you'll see a big difference. Those Spectre units are JUNK - the wraps should be tight next to each other, with no spaces between the windings. That's where part of the problem is. Also, the fewer the number of windings, the less overall resistance the gauge will see, throwing off the readings there as well. I ended up using my old sending unit and using the plastic float from the new unit, but still had to bend the float arm a bit to get the old unit to read sort of correct with the new float.