96 Blazer mny trouble codes and Hesitating, poor gas mileage HELP!!!

I have a 1996 Blazer with the vortec 4.3L W-Code V6. This is not the one with the tuned runners that look like a corvette TPI system on top. It has a central throttle body on the center of the intake manifold. Now for my questions. I have had a service engine soon light on. I took it in to get it checked out and it had thrown a bunch of missfire codes and trouble codes. codes as follows:Po300, Po174, Po101, Po171. It also showed missfire #1 1222, #2 1053, #3 1181, #4 1736, #52282, & #6 4276 on the scanner.

Any ideas what this is all relating to?

I have changed the plugs, wires, cap, rotor, pcv, fuel and air filters.

At idle in gear the engine lopes a little. If I stomp on the throttle from idle in gear, it hesitates, pops, bucks, and then eventually will start to accelerate if I let off the gas. Gas mileage is about 12-13 mpg. I get a slight smell of fuel in the passenger compartment. They checked fuel pressure and it was within limits and did hold after shutting of the engine for a while.

Please help guys and gals.
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Replace your MAF sensor.

I know this response is probably well after the fact, but may help someone else later.
Do you have to hold the ingition to "Start" for a longer period of time than normal before the engine catches also? Mine was having this problem and chased ghosts for a while before I took my brother's advice, who has been an auto mechanic for almost twenty years, and changed the fuel pressure regulator on the back side of the "spider" manifold assembly. He told me I'd be better off changing the whole assembly due to the hoses from the injectors getting brittle and breaking. I inspected mine and found them to still be flexible and chose not to change them due to the expense.
According to my brother, three of the symptoms can be poor gas milage, missing and hard starting.

Replace your MAF sensor.
Does he have to replace it or can he clean it? I plan on cleaning mine right before winter.

The MAF sensor is fairly sensitive, but if you use caution, a soft bristled tooth brush, and a little bit of "brake cleen" you won't do it any harm.

The MAF sensor is fairly sensitive, but if you use caution, a soft bristled tooth brush, and a little bit of "brake cleen" you won't do it any harm.
That is what I thought......

Cleaned the MAF, no change. Had the fuel pressure checked. Good at idle, at speed, and after being off for 15 minutes.