3.23 Open 8.75 diff needs to go

I had 3:91’s in my 1971 340 Duster that I used to have, and now on my 1974 360 Duster, I drive to and from the track and sometimes to work, on the freeway, I keep it about 60 miles an hour 3100 to 3200 RPM with 28 tall tires. I love those 3:91s