Here are m current # and then that numbers changes with 5sp and 3.67 gears

current 3.07 and 4sp (1:1 trans ratio final) with 24.7 dia tires @ 75mph= 3132 rpms

3.67 with 5sp overdrive (.75 trans ratio final)= 2808 rpms

Here are gear change MPH with the 722.4 /3.07 @ 6000 rpms 1-4= 34/60/97/144

722.5 with 3.67 @ 6000rpms 1-5 gears= 31/54/83/120/160

722.6 with 3.67 @ 6000rpms 1-5 gears= 31/50/81/120/145

You can clearly see the 722.6 5 sp with a 3.67 rearend would give me a very nice quick ratio setup as well as gain better fuel economy in overdrive freeway cruising @ 70-75mph.