2002 Chevy Suburban misfires

A p0171 and a p0174 code usually means that either your Mass Air Flow sensor (MAF) is dirty, or your fuel filter is dirty. Change your fuel filter and run it about 1000 miles. Then change the fuel filter again. When you change it again save the fuel filter you take out. Run water through it and catch the water in an old can or large jar. Check the water for any dirt or stuff like that. If there is a lot of dirt in the water then repeat the process.
Do not use an air filter that requires oil to be sprayed on the filter--like a K&N filter. The oil gets on the MAF sensor causing hesitation and misfires. Even if you do not have an air filter like this, your MAF sensor is probably dirty. To clean it take it out and spray electrical contact cleaner or brake cleaner on it. MAF sensors are rather expensive to replace, so I would clean it first.
There also could be a vacuum leak somewhere down stream from the MAF sensor. Check the round gasket on the throttle body where the induction unit seals up against.

Also, your engine is not misfiring. A misfire will be accompanyed with a trouble code of P0300--P0301--P0302 -- etc. The last digit is the cylinder that is missing. A P0300 code is a general misfire.
Use a fuel cleaner with Tectron in it. Cheveron makes a cleaner with this in it. Tectron is the same chemical that the GM Mechanics run through your system and it seems to work the best.

Check for a leak at the intake manifold gaskets. In my personal experience the number one cause of P0171, P0174 is because of a vacuum leak. If you have checked all the hoses, you need to inspect the intake manifold. You can spray carb cleaner around the intake while the engine is running. If you hear a change in the way the vehicle runs, while spraying, you have a leak. Let me know if you have any other questions.
Dave

I agree with flexy5. This may be the problem. If you have no sucess finding a leak, you should realize that an intake gasket can leak on the underside also. Have a scan tool hooked up, and see if the MAP sensor is reading below spec. Which is 4.0 to 9.0 grams per second. If it is the intake gasket may be leaking where you can't see or hear it.