What are the negatives to buying a sub 100k mile 14 or 15 Chevy Z71? It looks like I may need one. Actual owners if possible please. But if a Ford owner just has to chime in go ahead. I’m a Jeeper anyway and can’t stand square headlights.

Make sure you drive it at ALL speed ranges. The 14-15 year models had problems with the rear ends not being set up properly and you'd get a helluva vibration a certain speeds.
In my 14, that speed was 48-52 mph.
Also a lot of the trucks with 20" wheels had a bad shake due to bad tires. I also had to deal with that. Personally, I'd look for a truck with 18" tires and wheels.
There's also a safety recall on the 14-15 year model for a software re-flash. If it hasn't been done, the truck can/will shut off sometimes when turning.
I had a 14 that had every one of those problems. I know plenty of other folks who've never had a single issue with theirs.

Thanks for those leads and info! Good stuff to know

Is some 15 models the entertainment “radio” has problems and does what ever it wants

I've had my 15 for five years and 102k now. Only problem I've had its a leaky radiator that we replaced under warranty and the famous infotainment screen that occasionally goes blank for an hour (or day) our so. It has the 20" wheels too but no issues there.

Had to replace radiator on a 16 tahoe too and torque converter and wheel bearings ...only new vehicle I ever bought and I've done more in repairs than any other one