After the dyno tune and assuming you still need more low end performance, have you considered changing your rear gears? I have a SB 347 with 3.5 rear and TKO500 with a very tall 5th gear, something like .62 final and I tach under 2000 RPM at 70 MPH! (22 mpg on the freeway!
) I'm thinking of going to a 3.70 for better city perfomance