Ok now im lost, I was working on my 89 firebird formula when my fuel gauge pegged out full, so i did some testing and grounded out the sender while plugged in and also unplugged and it dropped the fuel level to empty. So im perrty sure the sending unit is bad so replaced the sending and put a new fuel pump in since was out of the tank, but before i placed the new sending unit in i wanted to make sure the the gauge would work. So i hooked it back up and moved the float and worked great. So i put it all back together and and took down to fill it up but will only read 3/4 full with a full tank, And i made sure the tank was full. So now im lost, WHAT COULD BE WRONG????

 

Anyone