Definitely get the front wheels off the ground. A few other pointers... You will be "burping" a lot of air out of the lines. With the engine off and wheels suspended off the ground. Open the pump reservoir and make sure it is full. You will be turning the steering wheel to the right/left lock to lock to bleed. At this time you will notice a lot of Mercon V being burped out of the reservoir and onto your frame, etc.. You should double up some rubber gloves and using a hose clamp clamp the doubled up gloves over the power steering pump reservoir filler neck. This will keep the Mercon V in the pump and not on your truck. You will honestly need to turn lock to lock about 35 - 40 times to get all the air out. If you are still burping air out on the 40th time... keep going if you want a clean air free system. Otherwise you will be complaining that your pump sucks.
If you get all the air out you will be able to turn your steering lock to lock without effort with the engine running and truck standing still. If you get all the air out and can't turn lock to lock while standing still, your pump does suck.. get a new one. Actually both the pump and gear box suck on these trucks.. had to get that in.