Mazda b-series 4speed auto vs 5speed auto?

-I currently own an 87' Mazda b2000 2wd 5speed manual pickup. There is not much I don't like about my truck. However I am looking to upgrade to a Mazda b-4000 pickup(94'-99'). Mostly because I need 4wd for the winter and play and I would also like an auto transmission. The biggest difference I see in the 90's mazda's is in 97, they introduced a 5 speed automatic where as before 97' all the auto transmissions were 4 speed. I'm just wondering if there is that big of a difference especially in gas milage. In my truck now I can only go about 65. If I go any faster it really starts sucking gas. I don't want that. I want to be able to cruse at 75 no problem on the interstate. Can the 4 speed do this or not? Any other tips on these trucks is appreciated.As I know such a car cost a lot to insure. Check your insurance quotes for these cars before buing one - carinsurance.deep-ice.com