91mustangrunner

looking for some answers on why my gas gauge is not reading properly.. i went to get the tank replaced becasue it started leaking.. and then the sending unit was done at the same time.. they shop that did the work thought were was about a 1/4 tank of gas but was near full.... and a couple nights before that i thought i was on empty and i put in maybe 15-20 bucks before the pump kicked out like full..... this was in november before i stored the car and im takin it out of storage in the next couple weeks, weather depending.. but why is my guage reading wrong? it also goes up after i drive around for a bit.... and the shop that did the work tested a new float and it didnt change the guage either....

could this be a wire somewere or the guage cluster itself??

thanks for any help....