gas gauge reading when full but goes down quickly

autoxcuda said
Get a picture of that one before you buy it. Very good chance it's the same as the cheap "chinese" ones.

Just look at your old sender, next to the new ones. They are designed very different. Much beyond the ohm reading.

The difference in the senders design or shape is in year models. If the OEM sender is 1973 or later It probably will be identical to aftermarket. Well almost. The very cheapest aftermarket sender has a plastic float.