2004 gmc sierra 1500 4.8 was stalling, had codes read, chanaged gas cap and mass air flow sensor, cleared codes. ran great for few hours.

check the link

https://www.google.com/search?q=2011+%22gmc+sierra+1500%22+iat+sensor+location

and what they look like

https://www.google.com/search?q=2011+%22gmc+sierra+1500%22+iat+sensor

..

With key off unplug the mass air flow sensor and try to start the vehicle. If it starts and runs fine, try cleaning it with mass air sensor cleaner, and plugging it back in. If cleaning doesn't solve the problem it may need replaced.

The Mass Air Flow (MAF) sensor is located in the stream of intake air and measures this intake flow rate by measuring a part of the entire intake flow. It is what they call a hot film and is supplied with electric current from the Engine Control Module (ECM).
The temperature of the hot film is controlled by the ECM to a certain extent. The heat generated by the hot film is reduced as the intake air flows around it. The more air, the greater the heat loss. Therefore, the ECM must supply more electric current to maintain the temperature of the hot film as air flow increases. The ECM detects the air flow by means of this current change.
The OBDII people suggest that before you replace the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with compressed air or by using a cleaner on the mass air flow sensor. Truly, all that may be wrong is a build-up of dirt.Unfortunately, in your case, replacing the Mass Air Flow did not work.After replacement, did you reset the code and drive the vehicle?.
I suggest you replace the air filter and check for intake air leaks.YouTube has some good videos on how to do this, one by Eric the car guy and one by Scottie Kilmer https://www.youtube.com/watch?v=9CPqbaSgcokhttps://www.youtube.com/watch?v=zMok2y05jNE

Have the fault codes read. Replace the faulty units with
genuine one because most aftermarket units are not set for OEM cpu units and are not completely compatible.. Check for mass air flow sensor fault.

Clean mass air flow sensor with a nonchlronated brake cleaner,install new air filter and check all vacuum lines for leaks then check for vacuum leak around or at intake manifold.Code P0140 is for mass air flow sensor code P0300 is a multiple misfire which more than likely is a vacuum leak possibly intake manifold gaskets leaking.

May be a problem with the mass air flow (MAF) sensor - I would check the readings from it to make sure it is working properly. It is very sensitive to fouling which can cause this problem.

starting definately has a lot to do with the crank/cam position sensors, but it wouldnt have nothing to do with hot or cold weather, oxygen sensor will make the vehicle run too rich if its out, you will smell fuel very strong out the exhaust, that could make it run sluggish also, and usually if the mass air flow sensor goes out the vehicle wont start at all...

i have a 06 sierra that done the same thing and it was the distributer gear stripped

check mass air flow sensor