I am thinking the gauge is working OK, but when it reaches 3/4 full then it acts like it is running out of gas, but I go to fill and tank only takes like 4 gallons.

Tank capacity is 16.9.

So maybe from the car sitting so long, the scrap at bottom of the tank has clogged the new filter.

I forgot to mention I replaced "in-tank filter"- part of Fuel Pump Assembly when I replaced fuel pump motor.