I'm glad you stumbled on the fact that the wrong temp sender was in there as even with your (posted) readings I might not have caught that. On the tank if you (1) pull the blue wire L connector off of the sending unit threaded stud and ground the female connector to a KNOWN good ground & the gas gauge pegs (key on) then the problem is at the sender. (2) plug the female L connector back on to the threaded nipple & key still on & run a ground from the sender short metal nipple to batt neg or a KNOWN good ground & see if the gas gauge reads correct. If you peg the gauge do so as briefly as possible just long enough to confirm what it is doing. (3) if so get one of those short metal factory pieces with clips on each end to connect the nipple to the metal fuel line a few inches away to restore the ground (4) if no reading then siphon some gas & pull the sender. (5) you might ohm the threaded nipple to the sender round circular flat before you pull it & see what you get & note how much gas you have in there right now