I know there are a lot of P0174 threads but mine seems to be slightly different from what I've seen on a search because I'm NOT getting a corresponding P0171. Details: 2004 Suburban 1500 LT, 4x4, 5.3/4L60. Currently at ~ 171k miles. This is my daily driver. Back when I got the truck in December of 2015, it started throwing both P0171 and P0174 codes right away. Took it back to the dealer and they diagnosed it as a failing intake manifold gasket. Gasket was replaced by dealer at their cost. This was at 136K miles in January of 2016. The truck has thrown NO codes since then, 2 1/2 years ago. Truck is my DD but is also used to pull a camper. For 2 years we pulled a 2,000lb [email protected] camper, but in January of this year we upgraded to an R-Pod 179, loaded weight is estimated at 3500 lbs. We live in Colorado and routinely take this combo over 10,000'+ passes without any issues. Coming home from a camping trip, after several hours of driving on a long, relatively level highway, I got a CEL. Checked it (Scangauge II) and it showed P0174 only (no P0171.) I reset the code and kept driving. No changes at all in vehicle performance. After returning home, I drove the truck normally. Changed the oil on Saturday, using "high mileage" 5w30 and a new filter (Fram heavy duty.) Was not able to change the air filter because they didn't have one in stock. Tuesday, driving around in hot, heavy, stop and go traffic, get a CEL again. P0174. I reset it, and 5 minutes later it comes back on. P0174 again. Reset again and it's been fine since then. The P0174 seems to come on after long, hot days on the road. Next week I'll be taking the trailer over 11,000+' Berthoud Pass. So, not wanting to just throw money at the problem, what is the consensus on what I should do? Clean the MAF sensor, maybe replace the air cleaner and see if that fixes it? Air cleaner element was last replaced probably 2 years ago so even if it looks clean I'm inclined to just go ahead and replace it. How likely is it that the intake manifold gasket failed just 2 1/2 years after being replaced? Or does it seem that it's likely NOT the gasket since I'm only getting the P0174 and NOT the P0171? Thanks in advance for any advice!