Running the numbers, I am going to try for an apparent tire size of 37 inches in diameter. That should give lockup in 4th at a bit over 35 MPH at an engine speed of about 1100 RPM, and 5th gear at 43 MPH at an engine speed of about 1190 RPM.
The 4.7L engine in my Dakota has a fairly respectable torque curve. The 4.7L in the Durango, being a next-gen Corsair with higher compression and two spark plugs per cylinder, would likely have an even better torque curve. At least, that's how I'd interpret my Durango's better response and performance over my Dakota's engine.
