Fuel Pump?

I have a 2001 Chevy s-10 6cyl 4wD with 72000 miles. When the tank gets to less than half full, it occassionaly lugs and takes a couple of turns of the key to get it started, unless it was just turned off. From reading your posts, it sounds like the fuel pump. I just spoke to a mechanic on the phone. After describing the problem, he said I should bring it in for a diagnostic check. He said that the check engine light should come on if the fuel pump is bad. My check engine light is not coming on. Would the check engin light come on if the pump was bad? Should I spend the money for a diagnostic, or just replace the fuel pump myself. It is a $370 part and I just want to spend my money wisely.
Thanks.