1996 K1500 Burb' running slightly rich

I have a 1996 K1500 Sub that maybe has a little bit of a problem. It has the 5.7 Liter Vortec. I think it is running slightly rich. There are no trouble codes, I have replaced all four O2 sensors with Delco ones, the fuel injectors have been replaced with Delco one's in the past year. It smells like unburned fuel when the vehicle runs. That and my gas mileage is poor (I know, I know it's a Suburban, but it's getting worse than my 93' did and this one has a K&N intake). There is no visible smoke, but it does seem to leave a SLIGHT film of soot in the exhaust pipe. I have heard that it may be the coolant temperature sensor causing the problem. It's a cheap part so no harm nor foul, I just wanted to get some opinions. Also, would a bad cat converter cause a raw fuel smell? The two suggestions I have had so far is the coolant temp. sensor, or maybe a malfunctioning fuel pressure regulator. The vehicle runs great otherwise, no problems whatsoever. Like I said no codes. Thanks!