Engine Performance problem
1999 Chevy Suburban V8 Four Wheel Drive Automatic 174000 miles
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My wife has a problem with her suburban. When we drive it for a while it seems to lose power, adn will eventually stall if we try to climb a hill with it. It coughs and pops when this happens. At first i thought it might be a plugged convertor, but it will run good on level road, do 65 plus and doesnt get hot. It recently started not starting after a 5 min run, and even in the morning it cranks hard and wont start. I have also noticed a fuel smell around the vehicle. I have changed the fuel filter. and checked for codes. ( none present) I pulled a couple of the plugs to check them and it looks like the engine is running a little rich. the plugs have black on them . What do you think it could be? Im a heavy truck mechanic and am a little weak on car diagnostics

I would check the fuel pressure regulator and also check the map sensor.

http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm