I think a decent exhaust system with some headers and a chip programed for what you want will help. Supposedly, a composite upper intake '02 and later Ranger (or '01 and later Taurus/Sable) is good for a few more ponies too, although I'm not sure where in the torque curve that occurs (you will need a TB, air inlet hoses, clamps, throttle cable, etc. from the donor vehicle to make it a complete bolt up mod).

I'm not a big fan of K&N filters and intakes either, more drawbacks than benefits (perceived) IMO.

A 4.10 rearend can be found in a junkyard cheaper than $1200.