6.2 diesel , sm465 4 spd. , 4.10 gears.... Wheres the sweet spot ??

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Im thinking of setting my 6.2 diesel in my dually.. For reasons of fuel economy..As title states its 4 speed and 4.10 gears (235/75/16 tires) The only trucks ive driven are the military trucks with 4.56 gears or trucks with the 700r with overdrives. Never 1:1 with 4.10s..So those of you that own them, what can i expect to run comfortably without screaming or being against the governor while driving highway trips? RPMs at say 65mph. Many thanks.. My big block does great and I know will out-perform the 6.2 but i mostly use it local so im thinking local fuel economy