Changing Sending Unit

After the addition of the ground strap, my fuel gauge still isn't working properly. On a full tank, it now only reads 3/4 full instead of the 1/2 full without the ground strap. Anyways, I have a new sending unit waiting to go in. Does anyone know if this can be changed without pulling the tank? The car will be on a lift tonight, and I'd love to change it without pulling the tank. 68RR btw.

Thanks.

NOt an expert but you will have to drain some gas if
it's that full. I don't know of any that can not be
serviced in the car.

Sounds like it's not the sender BTW. Might be the power wire to gauge. Same problem with my Dart and I know that's what it is. Old cars and too much resistance etc. You can try to trick it by bending the float arm a little in some cases.