I agree with Daox. If you're not at peak BSFC efficiency, press the pedal harder until you are. Then use micro-glides to control speed.
I would use 5th. Even running 3000 rpm is a killer to mpg, and anything higher (4500!
) is even worse.
75% LOD should correspond with about 12 psi MAP if your car reads that better than LOD. Edit: I saw Daox's comment about MAF. Not sure what advice to offer there.