Wikipedia lists the engines in all the Av’s.
this is a rundown of common problems:
How reliable is the 5.3L Vortec engine? Read about common problems like AFM, oil consumption, spark plugs, fuel pressure regulators, and more
chevytrucks.org
If you want power, I’d stay away from high-mileage L76 engines with AFM that were fleet or rental vehicles early in life. The L76 is the 6.0 gas engine. I ended up w/ the 2500 with the L18 engine. That engine is unstoppable if it’s maintained.
I’d Carfax any L76 truck, or check service records (haha! I made a funny) to see if they had a reputable place disable the AFM and replace the camshaft early in the engine’s life. Some of them you can tell they disabled AFM cause there’s an AFM disabler module plugged into the obd port that has to be there-blegh.
AFM tries to save mileage by only firing 4 cylinders instead of 8 when lower power is called for. The first engine that had AFM on the Av was in ‘07, I think? Maybe somebody can confirm or correct that.
There are lots of prob’s with AFM. The mileage gain is only about 10% because you still have to lug around the weight, and push a boxy truck through the air.
also Uneven combustion makes the engine heat up unevenly, over and over again. This sometimes make gaskets fail early, screw with the truck’s timing and wear down the camshaft prematurely. Check the service record for a camshaft replacement (not an upgrade) under 75k miles. That’s a huge clue that AFM altered that vehicle’s timing and caused engine components to bang in that camshaft until it was pitted and unusable, or even bent. You just spent all the gas money you saved on an engine rebuild.
I test-drove like 3 of the 2nd gen trucks with the 6.0 in them, thinking I’d get maybe the gas alternative to the duramax Silverado. They’d be better ‘cause they’re newer than first-gen, right? Newer is better... Well, not in those two trucks. Both of them had replaced camshafts before 70k. First one had a pretty big vacuum leak around the intake, and the rear seal had popped on the second one.
Of course, many people might have a great experience with the 6.0. That said, being around these trucks for a lot of years, plus experiencing those test drives, made me think the risk isn’t worth it. More experienced Chevy guys than me tell me “walk away” from the old L76’s. FWIW