I have been looking to change the rear gear in my 69. It is a 12 bolt positraction. I'm looking at a 3.42 gear and most seem to say the 3.42 is cheaper than say a 3.55. I guess I'm just courious why is the 3.42 cheaper???

Simply supply and demand, a 12 bolt 3.42 gear is a very commonly requested gear set, therefore a lot are manufactured, stocked, and marketed competitively priced in name brand and generic boxed sets.
Terry

I think it is easier to set up the gear cutter for the 3.42 because other GM rear ends also use the 3.42 ratio. The 8.5, 7.5 and 9.5 all use a 3.42 and those rear ends are still in production. I'm not sure, that is just my theory.

cuz it is the most awesome gear ratio around..