I had a leak around the fuel tank sending unit. The car ran fine. After my mechanic replaced the unit and the under floor fuel filter, I could not start my car. He then replaced the under floor fuel pump. It now starts often with difficulty. The gas gauge was on empty and the engine missed between 1200 and 1800 rpms. I filled tank with 7 gallons of gas. 10 minutes later the gauge read full. The car now does not miss at all. It appears that the gauge reads twice the used fuel. Whenever it reads near empty the engine will again miss at 1200-1800 rpms. At 70 mph and a gauge that reads empty I started to loose power and thought I was lucky to get to the gas station before I "ran out of gas" and filled up again with 7 gallons of fuel. What gives? Bad new sending unit? Bad in tank pump? Crud in tank? Help!