Chevrolet: 87 monte carlo keeps stalling, gas co, water pump

Question
hi, I've got a 1897 monte carlo that keeps on stalling if I come to a stop or if I put it into drive or reverse after I start the engine. I just had the water pump replaces and the problem seems to have occured since the water pump was replaced. I'm am not sure if this is an exuast problem, fuel pump problem or sensor problem. My car is a 4.3 liter v6 if that helps.  

Answer
Mike ,
   Have you changed gas brands ? try a can of gas treatment to the tank. It could be the fuel , or a adj. or a sensor , put the gas treatment in and try differnt fuel first. the gas co.s are putting alch. mix in the gas. you might  have a bad load of gas , try that first it can not hurt your wallet any way.