I have a problem going on with my 2006 Chevy Impala, it's the Police Package, it has a 3.9

A week ago my engine light came; I freaked out my husband on the other hand said it was minor. I finally took to Advance yesterday, let them pull the code - code is P0171 BANK:1

Looked up the code and found out it could be numerous issues.
Now, every now and then since that light has popped on I have noticed like a quick choke or hesitation whatever you want to call it when it's going about 65-69 and now....normally in the past, if I gassed it too hard the tranny would shift rough, I mean rough, but I could turn the car off, turn back on and it would reset itself I'm assuming. Now, like this morning, car sat all night right? I turn it on start to head down the road and it's shifting ROUGH but a couple miles down the road it smooths out?

My husband seems to think that the code could be from a clogged fuel injector, so he told me to put premium gas and a fuel injector cleaner in it (I did) last night, I don't know if that could be the issue.

Please any advice or suggestions would be greatly appreciated.
It has 157,472 miles on it
New tranny was put in at 93K

 

OBD-II DTC: P0171 System Too Lean (Bank 1)

Try cleaning your MAF(Mass air flow) sensor