Scott, don't know why you can't find any coils that are heaftier than 450#s, but you probably do not need to go any higher. I am using 400#s on my 2600 # truck and they are fine. There is a couple of things you need to consider. First, the 450# spring rating means that 450 #s will compress it one inch and you really want more compression than that. Second, set your ride height that you want, measure the distance between the coil seats, then buy the spring that will fit in that distance based upon the amount of compression you will have with the weight of the rear of your truck (close to 40 % of your total weight). A good ride is a combination of the correct spring load and shocks. Since you are using coil overs, then you probably want to install them so the unloaded ride height at 1/3 compression of your coil over.