Is this an aftermarket gauge sender? I ask because those must be adjusted carefully for the internal height of the tank or the readings will be forever wonky. There are two adjustments: the position of the sender body and the length of the pivoting arm. Ideally, the sender unit must sit so the pivot point is midway between the bottom of the tank and the top...in the AD this is usually 5.5" from the top. Then the length of the float arm is 1.068 times that 5.5" measurement or 5 7/8" from pivot to midpoint of the float. If you have everything set up that way, you'll be good.

If you want a sender that is designed to last and to be accurate, here is the best option I've found: eBay seller's ID is renbusan and the 0 to 30 ohm sender he sells was made in Taiwan and designed by somebody who knew exactly what they were doing. The good points: wiping surface is flat and not arched, contact fingers are metal and won't wear out as fast, resistance compound is poured in place on the outside of those contact fingers so it isn't subject to friction, body is either nylon or hdpe...maybe delrin or something that won't degrade in ethanol fuel and the price is good/free shipping. Here's a link:

https://www.ebay.com/itm/261122347319?hash=item3ccc1ad137:g:FBgAAOSwpPVgBuwZ

Good luck

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end