fuel questions

[texasfunk]

here lately the truck has been wasting ALOT of gas, its a 355 with an RV cam, 750 double pumper, and vortec heads, it is an 87 so it hasd the in tank fuel pumps, it has a CHEAPY mrgasket fuel pressure regulator on it, and i thought turning it down id lose performance, but gain some mileage, but it seems not to change, the truck is definately slower, but wastes about the same, the fuel pressure reg says NOT for use on Fuel injection, and for that reason has no return line, i am going to buy a fuel pressure regulator that has for a return line, and im wondering if this might help with the MPG issue? it seems like it is wasting WAY more then it should being its not a big cam, and has stock gearing and a 700r4 with overdrive, it uses abt 1/2 a tank every 120 miles, which is the distance to and from school, can anyone help? tyhanx in advance