My 1992 Mustang GT started bucking under throttle a few months ago, at first only doing it once in a
while but continued to get worse. I decided to replace the fuel filter, plugs, wires, cap, and rotor but the problem continued. I then took it into the shop for diagnosis and they told me it was the distributor so I replaced that as well but the problem continued and then the car completely died. I found that I wasn't getting spark so I changed out the ignition module and coil which fixed the spark problem but the car still wasn't getting fuel. At that point I replaced the fuel pump relay but same thing. I then replaced the fuel pump with 255lph unit because I figured if I have to do the job I might as well upgrade... Long story short it now runs faster than it ever has but is getting horrible gas mileage (like 4mpg tops). My timing is set at 13 which is exactly what it was at before. It idles fine (around 1500) but seems to have a slight back fire at the low end when you initially accelerate. I checked for for fuel leaks and can't see any, although when I was filling up, it didn't warn me it was getting fuel and gas started to spill out so I got under her and re tightened the rubber piece that bolts up to the car where the pipe initially comes down from the hole to the tank... I can't see that any gas is leaking from any of the lines and I followed the write up on american muscle to the t. Am I missing something here or is it the pump?
while but continued to get worse. I decided to replace the fuel filter, plugs, wires, cap, and rotor but the problem continued. I then took it into the shop for diagnosis and they told me it was the distributor so I replaced that as well but the problem continued and then the car completely died. I found that I wasn't getting spark so I changed out the ignition module and coil which fixed the spark problem but the car still wasn't getting fuel. At that point I replaced the fuel pump relay but same thing. I then replaced the fuel pump with 255lph unit because I figured if I have to do the job I might as well upgrade... Long story short it now runs faster than it ever has but is getting horrible gas mileage (like 4mpg tops). My timing is set at 13 which is exactly what it was at before. It idles fine (around 1500) but seems to have a slight back fire at the low end when you initially accelerate. I checked for for fuel leaks and can't see any, although when I was filling up, it didn't warn me it was getting fuel and gas started to spill out so I got under her and re tightened the rubber piece that bolts up to the car where the pipe initially comes down from the hole to the tank... I can't see that any gas is leaking from any of the lines and I followed the write up on american muscle to the t. Am I missing something here or is it the pump?

I really don't want to have to drop the tank for a third time because I missed something.