Revving 4000 rpms on the highway

Do you understand how to manually determine rear gear FOR CERTAIN?

If you don't know if it's limited slip, jack up one wheel with front safely blocked, and with transmission in neutral, see if you can turn the jacked up tire. If not you have limited slip and you must now jack up BOTH rear tires

With the one jacked up, assuming no limited slip, watch and count the driveshaft turns as you turn the tire TWO turns. This will give you the ratio

If it is limited slip, turn either tire ONE turn and count driveshaft turns. Same thing. You can easily estimate between 3.55/ 3.91/ 4.11 by being careful