Fuel sending unit? Getting wierd OHMS reading.

[rscam]

I have put a Jeep tank in my stepside. I have been driving it for a year now. The fuel gauge is off because I bought the wrong gauge to match the sender. I am wanting to straighten it out now so I took out the tank and sender and measured the resistance. It shows about 6 ohms full and about 28 ohms empty. I move the float and at about 1/2 tank it still shows about 25-26 ohms. I am at a loss. The number on the sender that came with the tank is a Jeep replacement number. 5357373 K It is a 73ohm empty 23ohm half and 10ohm full sender. I bought an aftermaket gauge the is supposed to have the same values. When the gauge gets to 1/2 it will not go any lower. Even if I am out of gas. Looking at the readings I am getting. The empty seems about right at 6ohms compared to 10. The half seems to be about right at 25ohms compared to 23. I just want to know where the 73 ohms went. I guess the sender is bad. Any ideas??