The 700R4 is the reason for your good mileage.I am running a 350SB,with a 700R4 and 3:90 rear,and getting 20 MPG.The 4 th gear in a 700R4 is about .78 to 1 ratio,whereas the 350 turbo hydramatic is 1 to 1 in high or 3rd gear.What is the gear ratio in your rearend?Nothing like an overdrive tranny for fuel economy.
