davester

consider doing electrical testing? I would guess some power or ground wire/connection has a problem. alldata.com has wiring diagrams, connector pinouts and diagnostic procedures you can use to find where the problem is.

can you tell if the reader is actually trying to get codes, and the pcm is reporting none, or is your reader just silently failing because it's not communicating with the pcm?

are there any codes? with lots of rust, perhaps disconnect/clean both sides of the connection/examine cable ends (the wires) for corrosion going into the sheath & replace if necessary/reconnect ALL the power AND ground cables between the battery, engine, frame, cab, fuse box and starter charm.li (website) has a no-start diagnostic procedure you can work through to get it working.

I would expect that to be lift-kit dependent. If the kit has interference issues w stock wheels, then the kit/manufacturer should indicate that somewhere.

You mean besides the obvious, that the dfm lifters aren't using any oil to enable/disable them (they stay enabled, and behave like a conventional hydraulic lifter).

? You don't NEED to install new wheels or tires after installing a lift kit. People install lift kits in order to run larger wheels/tires, and then may need to get wheels with different offsets for these larger tires, so they don't rub.

not all plugs will be used. gm uses more generic harnesses that support most/all options, and if your truck doesn't have a specfiic option, the plug won't be used (commonly will have a dummy insert in the plug , or it'll be taped up, but some may just be left as is). But it's sldo possible some p.o. has installed the wrong/cheaper parts that aren't correct for your vehicle...

computer pulses the injectors by connecting them to ground (at least on the trucks), so they get constant power...

Different monitors do their test only under conditions specific to that monitor. you MIGHT find the drive cycle conditions for the monitor that isn't ready on this site: https://lemon-manuals.la/ If it's not there, then it should be on alldata.com for your truck, but it requires a paid subscription. And you need to know which specific monitor isn't ready.

No, you still have DFM. GM isn't shipping some w/o DFM. You have latched onto some internet BS.

Sure, but you can add all the physical stuff, wiring, switches, computer, relay, etc, the thing that stops it is the programming.

No, because GM still doesn't sell the programming update that allows it to work for trucks that didn't come with it from the factory.

There are no stickers in your glovebox?

Look at the numbers on the stickers in the door jam...

google "bathub failure curve". Basically, any part of the vehicle can fail at any time. It starts off as being more likely (early failure), then the failure rate goes down (but does not go to zero), then it goes up over time because it wears/ages out.