Call Uhaul and ask them the hitch height when the trailer is level. Then measure from the ground to your receiver. The difference in the two is the drop (or rise) you will need.
I think you will be fine with that. I can't remember if I got the 4 or 6 inch, but which ever it is it is perfect with my aluminum utility trailer. Two inch would never have worked.
When you hook up the trailer to the truck, the "nose" of the trailer should be down a bit...not level, and not front end higher than the hitch.
To be honest, the Ranger's rear is high enough that even thou a 2 inch drop might be whats called for, a 4 inch will probably do just fine.
Your best bet is to measure it. Uhaul says that "optimal" height from ground to the middle of the ball is 18 1/2 to 18 3/4 inches.
I'm pretty sure I used a 4-inch drop to tow a Uhaul trailer a few times. However, even if I had used a 2-inch drop, I have an aftermarket receiver that sits a bit lower than the factory receiver, so your hitch would ride slightly higher than mine anyway and thus optimally use a little bit more drop.
Thank you gentlemen, Uhaul says it's about 18" & I just measured at about 19" so all good, I guess.
If Bob902 was good with 2" drop a 4" should be fine, 2" ball too, need to go buy that later today...
Looks like you got your answer, but I will add that I think you will be just fine. I recently towed the same trailer over 300 miles with my Tremor. The U-Haul location that inspected my trailer setup suggested the 2 inch drop hitch. Frankly I think it was not enough for the Tremor, but your truck should be one inch lower than the Tremor.
For reference, here is how the truck looked with the trailer loaded. I will probably buy a 4" drop hitch for future towing needs.