I calls BS, what's the miles on your A/T Z & what year,, mines a 2011 & never an issue with it in drive- always shifts @7500 by itself without going in limp mode( as spoke by someone else manual shifting) I've done that before too. From 60 with factory gearing: it should downshift to 3rd and wind up to around 85 & **** to 4th.... Have you ckd your tires or had them replaced lately::: different diameter tires will make it act stupid. Also- when was last time you serviced Trans or ckd fluid level.

Try to adjust your rev limiter maybe you had it set low.

You can adjust it using your left most fuel gauge selecting other options or maintenance. Try to play around with it and you can find rev limit.