I'm getting lean codes and my long term fuel trims seem really high, bank 1 16-19 and bank 2 is usually around 12-16. Sometimes at idle they both max out at 25. My oxygen sensors are both new (Vette rear sensors) and I can't find any vacuum or exhaust leaks, is there anything else I could check? I've also tightened all of the intake and header bolts down, I'm going to clean the MAF tomorrow and I've also ordered some GM fuel injector cleaner to try.

Its a L33 5.3l with TBSS intake and longtube headers.

 

How are you checking for leaks?

 

Just by spraying carb cleaner around suspected spots, I know its not the best way but I haven't found anyone with a smoke machine yet.

 

Fuel Pressure

 

I thought that also since it's on both banks but i'm getting 56 PSI at the rail.

 

Just curious.... Where did you end up with this situation? What did the issue end up being?
Going through a similar problem myself right now, frustrating, need all the help I can get...

 

What intake do you have? What year truck? Ive had these codes set for a few reasons, and seen them set on customers trucks.... My problem has been the intake adaptor piece that came with my k&n loosening up and creating a lean condition, have also seen where the intake gaskets when its cold leak and as they warm up and expand they seal again, if you still have a vacuum fuel pressure regulator pull the vacuum hose and see if it has fuel in it, and make sure the elbow isnt dryrotted or hardened and worn out, i have also seen a leaking vacuum booster diaphragm cause issues as well...

 

Sorry,
https://www.performancetrucks.net/forums/tuning-diagnostics-electronics-wiring-161/tvs1900-6-2l-12-yukon-denali-p0171-174-a-543368/TVS1900 on 6.2L (12 Yukon Denali) P0171 & 174
Intermittently popping a check engine light P0171 & 174 (Banks Lean) during long idles (once, maybe twice a month). LTFTs @ around 3 to 6 during throttle, 16 to 19 sometimes at idle & sometimes up to 26 on a large decel.
Stock Magnuson tune (stock Magnuson injectors and original pulley @ 5ish lbs. of boost, Volant CAI, original E85 fuel pump, stock exhaust, veh has 90k miles)
- Cleaned the MAF
- Checked for vacuum leaks, none found
- Reset LTFTs
- checked operating fuel pressure, stays solid 62ish lbs
need to get a wide band on it and see exactly where i'm at majority of the time....
Any input, greatly appreciated, thanks in advance!

 

Sounds like a seal getting worn out and intermittently throwing the code, or o2s getting fouled