What is the correct fuel pressure regular for me 200 Chevy Blazer?

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Dealership found fuel pressure regular loeaking internally, they replaced fuel pressure regular with part number 19210686. Before I brought the car in I was getting 10-18 mpg city driving with A/C. Since they have worked on my car I am only getting 12-14 mpg city driving with A/C on. I looked up www.autopartswarehouse.com and they came up with different ACDelco fuel pressure regulator parts; namely AC217388 and AC172251. What can be done to get my mileage up to 16-18 mpg city driving? I have been getting that mileage since I purchased the vehicle.