What is the rpm sweet spot for highway driving

For a mild performer like your mildly cammed engine has that see Hwy. driving of some distance, consider a O.D. Trans. The A-500 (904) has a .69 O.D. ratio.

3.23 X .69 = 2.22
4.10 X .69 = 2.82
4.30 X .69 = 2.96

Food for thought if the wallet can handle it.