down shifting ?

Because it's a manual transmission, you can force it into any gear you like at the risk of damaging the truck. To slow down from 10th gear and 55 mph to a stop, I would apply service breaks until we are down to 40 mph, downshift skipping 9th directly into 8th. Your Rpms will be on the high end of 8th. At 20 mph you can skip 7th and go down to 6th, and your Rpms will be high, on the high end of 6th (if you were up shifting , this would be the point where you shift up to 7th but remember you are losing speed and braking).

5th gear is very slow, if you are empty you could even take off in 5th but it wouldn't be pretty. Also, when the clutch is depressed you are basically in neutral even if the stick is in gear.