Bigger valves installed properly (deshrouded and good valve job)improves flow even through the same size port, in order for more air to flow through the same port it HAS to have MORE velocity, therefore a bigger valve will have more velocity in the port not less. Any one who beleives otherwise is it is very elementary physics not rocket science. Velocity at the valve will probably decrease but total flow will go up and that means you can make the same power with a smaller cam and a smaller cam will help MPG.

As for gearing, lug the snot out of it. My 5.9 in my 3/4 ton ram turns 1500 at 60 and gets much better MPG in OD than 3rd. You car is slightly more aero dynamic and probably lighter than a jacked up extended cab 4x4 3/4 ton and your engine is definately more powerfull even at those low RPM.

You definately do NOT need to be above 2000 for best MPG, mabey best passing power but it is bad for MPG.