Not sure if someone told you to buy the slider or not but it is certainly not necessary on a 6'6" short bed. now if you have something shorter than that, yes you still may need a slider ie a RAM 2500 mega crew cab would have an even shorter bed, like 6' I think perhaps even a little less..
I have a 2015 29.5BHDS with the Reese revolution also. My hitch is a Reese Titan 16k which I ordered the custom Reese wedge for. Did I need it probably not but I bought it none the less. Now when I picked up my trailer from the dealership in Indiana they installed the wedge that comes with the pin box which is the general purpose one size fits none wedge. I suspect they did not install it per Reese's instructions because I had a difficult time connecting and disconnecting. Once I got home to AZ I installed the custom wedge from Reese following their video instructions
http://youtu.be/f2JjHwssJos and now it connects and disconnects without a problem.