Desperate, you say? Swap in a TDI
For what it's worth, on a recent trip from Phoenix up through Misoury to Michigan we got 19.6 average over 5 tanks. On the way back we took I80 through Iowa/Nebraska to I70 and then down through Utah and averaged 21.7.
The way back was the time when the transmission crunched and groaned and we started looking thinking about nearby airports, so it may have been babied a bit more.
At 16mpg you could possibly change your plugs, advance your timing a tad if it hasn't been looked at recently, and drive a bit more carefully. That's probably pretty close to what it's capable of, though, sadly.