Hello guys. I have been reading online for more than a year trying to fix the issue with my truck. I have found lots of great info here and other forums, but I still don't have this thing fixed. I spent better than $5000 last year trying to fix it....Some quick specs and info: 2015 KR FX4 SC V8, tow pkg,120k miles, all the toys. I started noticing a vibration on the highway (75-80 mph cruise) some time back, but since the tires were getting weak I replaced them hoping the vibration issue would be solved (OE Wranglers). No dice, better maybe but not fixed. I read about driveshaft issues and put the GoPro under it and found no visible abnormalities. There was also a popping noise in the front diff or transfer case when in 4 wheel drive while turning on or offroad. My local dealer is somewhat useless, I have had to go behind them more than once and fix what they fixed, so I took it to a local guy with a good reputation after I did all I could do on the garage floor. I have replaced front hubs and IWE's previously, left front hub had a bad bearing. He found that the front diff bearings were bad along with the front driveshaft joints. He also found that the aftermarket hub had slightly different offset, so he got the store to swap it for an OEM unit. All this work (tires,diff,front driveshaft) did seem to get the job done. At less than highway speeds this thing rode and drove great again! But there seems to be another issue that was hidden by the other issues Again at highway cruise speeds I am getting a vibration that will vary in intensity, I have not been able to isolate the conditions completely but it seems to be worse under load. The shop has looked at it again and thinks that a rear driveshaft U-joint seems a "little tight". More concerning to me is the vibration/noise that i can isolate. At varying times on the highway a vibration turns into a low pitch noise, like something flapping in the wind. I have found that if I switch from "2H" to "4A" the noise and vibration seem to go away. I tested the IWE system by attaching a mity-vac to the hub side vac line and put a gauge on the supply side vacuum line. I drove the truck with the gauges zip tied on the cowl and a vacuum pulled on the IWE's to keep them disengaged. As I had the IWE system isolated from engine vacuum and the vacuum side monitored with a gauge, I could see that the supply side vacuum remained constant until I switched the 4WD system on or off. At highway speeds I got the vibration/noise as usual and flipping the drive selector still made the issue stop. To my knowledge, the only other system affected by the 4WD switch is the transfer case. My plan going forward is to get the rear driveshaft to a driveshaft service shop and have the balance/run out checked and the U-joints replaced. But that leaves the other vibration issue open potentially. I am open to any of you throwing out your experience with the same type of issues and how you solved them.
Just a little rant, my previous truck was a 2009 Lariat SC 5.4 4wd. I "sold " it to my son-in-law with over 210k on it and it is still going strong. IMHO the old trucks ride and drive much better than the newer ones and keep going like a cheap Timex. The tech stuff on the newer trucks is wonderful, but the other problems may not be worth stepping up. My son had a 2016 KR with similar issues to mine and just sold it rather than try to fix it (he previously drove a 2010 Lariat, 200k+ miles). He now drives a 2021 Lariat FX4 SPT SC Eco Hybrid with the 7.2KW Powerboost. That truck is amazing! The tech stuff is so far advanced from the old trucks it makes them look like dinosaurs and it rides and drives like the older trucks. A big improvement IMHO.

Sorry to be long winded on my first post. If any of you have information to share I would greatly appreciate it.

thanks,

Chris