intermittent check engine light

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

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.

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

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

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