4 speed OD with 3.91 gears

72 440 Duster with around 525HP at the crank, 391 in it know but am changing to 410 this winter, I only use fourth on the main HWY, over 70 MPH, 2400RPM at 70. It lunches hard at the track but I only use 1,2,3. as 3rd is suppose to be the fourth in a Regular 833, love mine as it gets way more street that drag. I still only get 10 MPG on the HWY.:cheers::cheers::cheers: