I moved the jack back 5" yesterday, used a 5" piece of 1/4" C Channel steel. Also moved the lower plate back. The gas tanks were moved about 3.5" back, also the tray had to be moved back which in turn had to be flopped to the other side because battery cables were too short to move battery to front tray. I will design and build a new tray soon, just was done screwing around yesterday.
Works great, can open the tailgate with no worries now. Not sure every manufacture (Ford/Chevy/Dodge..) all have this high of tailgate so it may not be the same problem for everyone.