new float, still bad guage reading??

[69 XCamper]

I replaced the leaky float in the gas tank sending unit. Tested the operation on the unit outside the tank by grounding it, and all works fine at the guage. But, when I install the sending unit, it only reads 1/8 of a tank when it should read close to full. I've removed & installed it three times & same result. And yes, I did check the float...it does float. Any ideas? I'm baffled.