The past 2 weeks my truck has been getting very poor gas mileage. on 2002 Chevrolet Silverado 2500 HD

It smells like it is running rich. Could it be the fuel pressure regulator. I've changed plugs and wires. not sure which way to go from here.

Asked by for the 2002 Chevrolet Silverado 2500 HD
Have it scanned with a real scanner, not a code reader and fuel system pressure checked.
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1 more answer , 1 more comment
you might want to get a mech opinion if your not equipped to handle suggested tests
'HAVE' it scanned!