I have jpx 900 forged irons with project x lz 5.5 and would like to know your suggestions on putting kinetixx ts-I in a R flex due to back issues

Well… the short answer is, that there is no problem doing what you propose. Both shafts are .355T shafts. But why are you making a move to a regular flex from a rather stiff 5.5 flex? What is your typical 150 yard club?