Agree, weigh your setup, axle by axle to know where you are
Also, with a guesstimated trailer weight of 6,000...you are most likely over the dead weight rating of your reciever.
Most Suburban OEM receivers dead weight rating is 500 lbs
To check what diff ratio, either check the RPO codes as others have recommended.
If bought used...previous owner(s) may have changed the diff ratio
Consider tieing a length of string to the driveshaft.
Then roll the vehicle one tire rev. Use a valve stem as a datum.
Then count the number of string turns. That will be the diff ratios whole number
Fractions if a turn left will be the diff ratios fractional number.
3 whole turns is a 3.xx
3/4 of a turn is x.73
Remove the string...
Edit...assume you are NOT towing in OD if no tow/hail function on your dash