Less than 20,000 miles since 2014? You've probably got significant corrosion in there from it sitting. Drive it more, it'll likely track down.
Maybe not "this" ....
Theory 1: not driving enough caused this wear issue
Theory 2: head swap caused this wear issue
Theory 3: something other than T1 or T2 caused the wear issue
Facts we can take from the limited info given:
- From 2000 (new) to 2014, they drove about 100k total miles; averaged 7k miles per year over 14 years. The wear in 2014 was perfectly fine all the way around. We'll presume the wear was good for whole 14 years.
- Then from 2014 to 2021, the driving went down a bit to around 4k miles a year. But wear went WAY up somewher in that time frame.
- Driving distance is around 3.5k miles annually over the last 6 months (1.75k miles over roughly 6 months). Wear has stayed "up" over the last 6 months.
So the major wear-rate change happend somewhere after 2014 and before 2021. That aligns with the major mechanical work, but I find it hard to believe that changing a head caused a cylinder/piston issue. There's not enough Si to blame it on dirt intrusion from the work done, nor an intake tract leak either.
I also find it hard to believe that going from 7k miles a year (a fairly low use rate), to 4k miles a year (even lower use rate), suddenly caused a HUGE spike in piston/cylinder wear. That is a massive spike in wear to blame solely on a slightly-lower use of the vehicle. Think about the "you're not driving it enough" logic suggested in the above posts ... So the owner drives it 40% less, but sees wear jump up 17x higher??????? Nope - I don't buy the "drive it more and it will be fine" logic; that's absurd.
With two UOAs being 7 years apart, it's just too hard to know "when" this wear issue really occured. Did the wear-rate change happen before or after the head work? None of us know for sure.
I think what we're looking at is "coincidence". I believe there's a piston/ring/cylinder issue that just happened to occur somewhere in that same 7 year interval where both driving distance dropped and head work was done. However, because there's not a good history of the wear-rates (7 years between UOAs), we can't say "when" it happend with any accuracy. Just because there is correlation between the head work and the wear-rate change, does not automatically mean the head work caused the wear issue(s). The two events coincide, but that does not mean one caused the other. Same goes for driving less; that happened somewhere in the same 7 year time-frame, but driving less should not cause wear to go obscenely high.
Theory 1 fails to make sense ... driving 40% less should not cause wear to shoot-the-moon by going SEVENTEEN TIMES higher.
Theory 2 fails to make sense ... there's no logic to saying a head-swap should result in massive piston/cylinder wear.
Theory 3 makes the most sense; something other than T1 or T2 caused the wear to spike during that time from 2014 to 2021.
One should never confuse correlation with causation; I've said that repeatedly over the years here at BITOG. But, one should also not confuse correlation with coincidence; just because two or more things occur at the same time, does not mean one caused the other.
My opinion ... I'd investigate the issue of a cracked piston, or whatever else these 4.0L engines may be known for in the piston/cylinder area.