Chevrolet Astro

I own a 1999 Chevy Astro van AWD V6 Vortec (72K). I recently had repair work to my fuel gauge since it was not registering how much fuel was in the tank. My question is : Ever since I got the work done the van is only getting 200 miles or so to the tank of fuel. I was averaging 350+. Any thoughts would be appreciated.
February 17, 2007.

Thanks for replying Tech1. I should have mentioned that the fuel pump was replaced. It was replaced because the sensor that relays how much fuel is in the tank went bad. I was told that the sensor could not be replaced but the whole fuel pump must be replaced. I figured it was close to 100K so why not replace the whole thing. Since then the miles per gallon went downhill, really bad. I was thinking about doing the basic (spark plug, wires, etc.) But I do not understand why the miles per gallon went down. Also nothing else went wrong with the van, like dash lights or anything else. Anyway thanks for replying.

Feb 17, 2007.