intermittent check engine light

[motorsports12]

i have a 2012 gmc sierra 2500hd wt with the 6.0l gas engine (flex fuel) that just turned 100,000 miles - it has been really cold weather off and on so not sure that has much to do with this but a week ago the check engine light came on - put it on the obd scanner and got code p0171 and p0174 both banks running lean - one of the fixes was to clean the maf sensor - so i did - and for a week the problem went away - thought it was fixed but it came back on - i just put gas in it this evening and thought i would wipe the ring off where the gas cap seals - the check engine light went off again

could it be i have a bad gas cap or a bad seal at the gas cap - is the maf sensor bad - do i have some other issues like an o2 sensor going bad or maybe a vacuum leak - the only thing i have done to this truck (only had it for 6 months) is change the oil and the air filter and just recently had to change both head lights (reason i bring this up is because i had to remove the air box on the passenger side (could there be an issue there since its hard to get the box back into its rubber push grommets) and a battery tray on the drivers side

not sure my problem is fixed but wasnt sure if i should try anything else - i use this truck to pull a trailer to and from the race track so i need to make sure its good for the season with racing season about to start

[Tech II]

P0171 or P0174
Too much oil in K&N filter
Bad MAF
Vacuum hoses split, kinked, or improperly connected
Insufficient fuel in the tank
Low fuel pressure.
Fuel contamination. .
Malfunctioning fuel injectors.
Missing, restricted, or leaking exhaust components.
Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
Leaks in the air induction system and the air intake ducts
Kinked or improperly routed fuel injector lines
Missing air filter element
A cracked EVAP canister
Evaporative pipes obstructed or leaking
Leaks in the crankcase ventilation system.

[motorsports12]

is there a different code for the gas cap?
looking at new gas caps they are vacuum caps for the flex fuel vehicles - since I have put gas in it ... so far the light has not come on and it seems to be running smoother

[Tech II]

Gas caps usually cause P0440, P0442 codes....

It is part of the EVAP systm.....