I got a similar notice today when I started my GX BUT I also noticed the open door signal as you have on the speedometer. I checked my drivers door, passenger door and thought it must be the back hatch as it was the last thing I opened the day before. Still had the red open door and a beeping noise. Then I decided to check the rear hatch window. It was not shut for what ever reason. After I shut the rear hatch window everything was back to normal. Check all four doors and hatch door and window to see if this fixes this issue.

 

The maintenance reminder comes also with doors closed, I was just too lazy to close the door for the picture.

I do not have an issue, as my reminder is 10k miles. others are having 5k reminders, the wrench/distance to service comes up every time you start the GX

 

I have only put about 500 miles on my GX and today the tool bar showed somewhere around 9200 miles. So I guess my reminder is 10k miles also.