My grandma's 1970s flour sack towels are still going strong while the new ones got holes after like 20 washes. Old stuff was just built different.

How big is your firebox though? That 20 minute thing works great on a big stick burner but my little Oklahoma Joe eats splits way faster than that. I got a guy near me who does the same thing, feeds it on a timer, and his brisket always has that thin blue smoke. What worked for me was getting a basket so the coal bed stays even, then I add one split every 30 to 40 minutes depending on wind. Wind is the thing nobody talks about, a breezy day will mess up your whole timeline. Are you running a water pan or anything to help even out the temp swings?

The "stopped pulling codes first" part is kinda risky tho. Codes can point you somewhere the test drive never will, like a pending misfire that only shows up under certain conditions. I do both, scan it quick then drive it, saves me from chasing the wrong thing.