wildcard

OK here the deal, I had an 04 ram 2500 quad cab 2wd with the six speed manual, Loved the truck but want a 4x4 so I sold it. (had the six speed because the auto transmissions seem to be troublesome on those trucks) Im now looking for a new truck and in my area the 07-08 with the 6.7 and auto are much cheaper than the older trucks with the 5.9 with either stick or auto. I don't know anything about the 6.7 or the auto trans used with it. please steer me in the right direction. my 5.9 never gave me a lick of trouble, always started even in minus 40 without plugging it in. what should I exspect if I buy the newer combo? I thought one of the ads say the 6.7 has a six speed auto trans? any info would be awesome, how's the fuel milage compare?