833 OD- what tooth setting 2 use

I am using a cast iron 833 OD in my 65 cuda. I have 3:73 gears and 24"tires. I currently am using the 32-38 speedometer setting on the cable connector but doesn't seem quite right. The other 2 settings are 26-31 and 39-45. Also my speedo sometimes runs smooth and other times it pegs all the way around to the bottom. My cable is new so there are no cable splinters in the housing. I have the tranny out replacing the TO bearing. Thought this would be a good time to make any changes. Any thoughts appreciated!