You have a Highlander truck! If you're not familiar with the Highlander special promotion package do a search on this forum as there is a wealth of information available. That's a very nicely equipped truck. My best guess would be a 3.07 open rear end with a Turbo 350 transmission as the SPID would normally denote anything different on the rear end ratio. If you put 275/60/15 tires on you will be at ~2500 rpm's at 65 mph. Check out these two links.
http://spicerparts.com/calculators/e...rpm-calculator
https://tiresize.com/height-chart/