'96 Voyager runs well but get bad mileage

I have a 1996 Voyager SE 3.3 with 208,000+ miles. My mileage wasn't what I wanted, 20-21 hiway, and my check engine light was on, for over a year. In the last two months I've replaced the EGR (cause of the check engine light), the spark plugs, plug wires and both Oxy sensors. My milage continues to drop. Less than 19 on the last tank, and this tank looks even worse. The engine starts in less than 3 seconds, it has power, runs smooth and idles smooth.

Whats going on? I was better off before I started.