if it was me, find and clean up and possible vacuum leaks, anything from old emissions things, to intake couplers.
Tune up, all the way around, from the fuel pump sock, all the way to the plugs and wires, to the air filter. Make sure everything is nice and clean and fresh.
get a fresh pcv on there, who knows how old the one on the engine is. that could make a decent difference all in itself.
Clean the MAF senor. I don't remember what kind of filter you had, but if it is one of the ones that is supposed to be oiled like a K&N, then either the oil itself can get through the filter and coat the MAF, or, if you don't oil it, then little bits of road grime can get through the filter and coat the maf
Make sure you are getting the correct fuel pressure, and not stuck at max psi all of the time.
I'd get a fresh o2 sensor on there, just to be sure, unless a wideband is in the near future.

Because you did remove those emissions, you should be running a bit rich. Remember, the stock tune is set up to have that little bit of extra air coming from the EGR valve and all of that. So once everything is all nice and fresh and in good shape, you should still be pretty rich. I found that I was able to run much more advanced timing because of that, and that helped even it out the mpg.
Ideally, you would do all of that nice "powder its nose" type of stuff then get some kind of tuning to bring the mix back down to where it should be. A wideband o2 sensor and a safc would go a long way. While normally, I wouldn't suggest a safc, since you don't have boost or anything like that to really worry about, you can get away with just a simple safc tune. All you're trying to do is get rid of the excess fuel anyway. But, don't just get an safc and run with it, you really need the wideband to tell you where you are at. It is really easy to over do it with an safc.