Hip knee running connection

Hi. I am lifelong runner , hiker, bicycle commuter & triathlete with a specific question re. hip replacement recovery and running. Had anterior hip replacement on right hip March 2012. Before that did a lot of triathlons. Good quick recovery & back to jogging by that summer but did not run seriously as we did international work a couple of years with minimal running/ competition opportunity, then I had series of small injuries (not related to hip); last year it was a broken arm when I slipped trail running! I  would like to return to long distance triathlons. However if I run more than 5 miles I get a “popping” in right knee. My physical therapist says it’s weak hips & gave me lots of hip strengthening work. I wonder if right hip perpetually weaker because of artificial hip& puts more stress on knee. Has anyone else in the community had this issue and do you have advice on how to specifically target/strengthen weak right hip?  I do not get these problems cycling, hiking or backpacking. I do best on trail running and worst on flat pavement; alternating some with barefoot/toe shoe running seems to  ease stress on knees. I thought about more work in minimalist shoes; something I could use for triathlons that would be easier on knees but easy to slip on? (unlike toe shoes which make you crazy in transition).  Thanks for all/ any advice!