..........I hope this hasn't been addressed in a prior thread, so forgive me if it has.

I have a 2020 TRD pro that I've put 11,350 miles on in just over a year.

A few days ago I reversed the truck down my driveway staying on the incline, and then put it back into 'drive' to go up the drive at a very slow speed. When I did so, the slip indicator light went on and I heard that grinding noise for just a second or two.
I took the truck into the dealership on Saturday and they looked at it over the weekend and today. They checked it out thoroughly and told me they couldn't find anything wrong.
They checked the VSC system, TRAC system, active traction control, hill start assist control system, etc: NO issues with any of them. They reassured me of this.

I haven't done any significant off roading yet-- in fact my first venture was set for next month.

Their diagnosis was that the rear tires simply are losing traction for that brief second going back up hill after the car has been reversed downhill, although the stock Nitto's still seem to have good tread.
Has anyone else dealt with this and are there any thoughts as to the cause (i.e. is this simply my rear tires starting to lose traction at 11.5k miles?). Do I need to be concerned and take it to another Toyota dealership?

Other this new issue, the truck has been amazing and running great and I've put several long trips on it.

No.

I do not believe you have any issues with the truck or tires... Vehicle stability control (VSC) is very sensitive on all 5th gen 4Runners and when you switched into the drive on the incline your truck probably rolled (moved) backwards a bit (inches..?) consequently triggering VSC... it worked as designed.

FYI: My truck does the same thing.

Mine also does the same if it detects the car going back just a little on a hill.

Sounds like your Runner is doing it’s job. I have a house in the NC mountains up really steep gravel roads with a steep gravel driveway. I exercise my traction control all the time, it makes some strange noises but I’m used to it by now.

thanks for the replies and reassurance, guys.

It's just that it's never happened before, so that's why I was a bit alarmed that it's only happening now with the same reverse, and driving forward on an incline (driveway)

This has happened to me a couple of times and I too thought something was wrong. As others have mentioned, the vehicle is just doing it's job. Love this beast!

Normal.