congratulations on having a great truck. the dana 60 axles are the holy grail of axles, offering more strength, durability, and optional equipment than any other. those axles are considerably better than the d44 and 9.25 that come with the 1500.

by all means plan your locker install and gear change at the same time, or else you'll have to pay for it twice, and its going to be pretty expensive as it is. For 35" tires, definitely go 4.56 or 4.88. just write down what your rpms are at various speeds now, and multiply it out to see what it would be with the different gears. it really depends on your driving habits. if your'e bound and determined to run 90 mph on the freeway, then look at what rpm you're willing to turn.