Interesting. Thank you for the info. I have the same stock 05 truck and have had the 5100 on since the stock red "offroad" shocks were obviously worn out (the "offroad" badge is only the addition of skid plates and red shocks). The 5100 were a HUGE improvement over stock in ride quality. I installed Riderite airbags to make it even better and have not had any problems. I learned the hard way not to inflate the bags to any pressure per say. I just have someone with a tape measure tell me when the top of the rear wheel well is the same height as the front wheel well. The first time I inflated them I tried to get the rear to stock (empty) height which caused severe porpoising.
The 5100 are all silver in color with no reservoir. When I bought them I was told there was no difference in valving, only that they had a longer travel length. I offroad so that is why I picked them. I may try the 4600 next time to see if it makes a difference.