I thought I'd just reinforce this; learning this has helped me massively understand how to expose properly, and if you don't have time/are in a rush - always, always, expose for the sky.
I think what the OP is saying is that the D750 is over exposing compared with his D7000 despite performing a hard reset on the D750. With the side-by-side comparisons it is obvious something is going on.
Yes but one can't compare two shots when both cams are set on A and using auto-ISO. Both don't necessarily use the same settings. The range of auto-ISO on both is hugely different, their native ISO probably too.
I just did with my D3300 vs D750. Both 24mm same aperture and "all go" on ISO and shutter. Then I put them down and pointed at the same object.
They used the same ISO which is to be expected since they're both of the same generation but the shutter was 1/30s vs 1/40s. I expect the difference between the D750 and the D7000 to be much bigger when you set half of the settings on auto.
The two cameras may very well both be set on auto ISO in Aperture Priority, but *if* they are both metering correctly and *if* there aren't any other setting differences, their metering should be quite similar. Generally meters are designed to meter as 18% grey so regardless of the ISO, they should be close in exposure unless there is a setting difference somewhere or if the metering is off.