How can I add a wedge to a U-haul ramp to avoid the step down from the truck bed?
On all of the rental trucks I've driven that had a ramp, the ramp could be pulled out a bit further and was able to be lifted up and latched into place at the same level as the inside of the truck, for exactly this reason.

U-Haul has a youtube video showing how to use the ramp; lifting the ramp up to the level of the interior is seen at around 45 seconds in.