I now have 5500 miles on this vehicle and I have been meticulous in monitoring the details of the performance and fuel economy and how every variable affects both. 87 octane has me just over 15.5 mpg, even with the new intake. 93 has me at 18. I manually calculated the usage as well. I'm going on pure numbers. This vehicle likes premium. 🤷‍♂️ This engine also has an 11 to 1 compression ratio.

Type: 5.3L V8Displacement (cu in / cc): 325 / 5328Bore & stroke (in / mm): 3.78 x 3.62 / 96 x 92Block material: cast aluminumCylinder head material: cast aluminumValvetrain: overhead valve, two valves per cylinder, variable valve timingIgnition system: coil near plug, platinum-tipped spark plugs, low-resistance spark plug wiresFuel delivery: direct fuel injection with Active Fuel ManagementCompression ratio: 11.0:1Horsepower (hp / kW @ rpm): 355 / 250 @ 5600 (gas – SAE certified)380 / 283 @ 5600 (E85 – SAE certified)Torque (lb-ft / Nm @ rpm): 383 / 519 @ 4100 (gas – SAE certified)416 / 564 @ 4100 (E85 – SAE certified)Recommended fuel: regular unleaded or E85Maximum engine speed (rpm): 5800Emissions controls: close-coupled catalytic converter, Quick Sync 58X ignition, returnless fuel rail, fast-response O2 sensorEstimated fuel economy2WD (City / Hwy): 16 / 234WD (City / Hwy): 16 / 22

 

It's a matter of cost per gallon vs miles per gallon and which is cost effective for you using regular or premium.
My lower horsepower '11 5.3 runs the same on either fuel mpg or power wise.
19 mpg on regular if I keep it under 60 with the AFM disabled. EPA mileage tests are conducted at 55 mph, that's where the estimated mpg numbers come from.
Throw that K&N in the garbage and put a stock paper filter back in. K&N lets too much dirt through it for a stock motor, stock filter and airbox flows way more air than a stock motor will ever need. K&N is for racing, those motors get rebuilt all the time so dirt wear isn't a issue unlike a street motor which we want to last 200k plus miles.
Lots of tests out there showing how much dirt they let through.

 

I have already replaced the K&N with AN AFe intake system. The K&N was a placeholder until I could replace the intake assembly. I don't believe that K&N filters cause any issues when used in a typical car. The factory paper filter is an inferior media and the intake assembly is extremely restrictive. I have watched the efficiency improve as I have made changes. Regardless of cost, I am going to feed my Tahoe the fuel it burns most efficiently. At 11.0:1 compression, I can see how this engine would like premium fuel. As for the older generation of this engine, I can't speak to the specifications. Until this point, I have only purchased Mopar. Thanks for the input. 👍🏻

 

oem filters are better; meet factory filtering standards. Many performance filters lead to dust out conditions. I have replaced many nissan mafs after owners went aftermarket or oiled filters. What i have seen is the factory filter element is dirty....after replacement at the next check, the new filter is clean...the maf screen is soot filled. gm maf have a burn off circuit so they are less effected but dust out is still a problem.

 

My 2021 Tahoe isn’t Z71. When my wife and I lived in two places until we found an apartment we were driving about 1000 a week and getting 19-20mpg regularly. Now we drive in town and we were doing 15-16. Suddenly it dropped to 12. I replaced the air filters and serviced it. But my tires are getting a little a little low on tread and I probably need an alignment. So, I don’t know. It’s getting warmer and the AC runs more now so that may be a factor.