My first 4 full tanks of gas in my rodeo varied from 16.5-17.5 depending on how hard I drove it. Then my alternator died and me and my dad pulled it out, had it rebuild, and reinstalled it.

Since then I have ran out of gas on the side of the road twice. The first time at 286 miles (13.6 mpg).

And yesterday I ran out again at 297 miles (14.1 mpg).

In between those too I filled up the tank completely at about 200 miles, but did not work out my mpgs for that tank.

I really dont know what could be causing this horrible milage and whatever it was happened between the alternator dying and getting fixed. I was thinking that maybe we could have knocked the timing off in the engine or hit the distributer, but really have no idea. It may have nothing to do with the alternators installation and maybe something else that coincidently started to mess up at the same time. Maybe I have a dead cylinder? I have not noticed any loss of power although I don't really have a means in which to accurately measure it and I have also been driving as conservatively as ever so that is also not the problem.

Any help is greatly appreciated.
Thanks!