So I went from a basically completely rebuild Fj60 (including the drive train) to a 2015 Jeep JK 4 door which I have own 3 years.
My Jeep has the hard top and I have not taken it off. Also 3.6L, 3.73 gears LSD, 6 speed manual with 33" tires, AEV 2.5" lift, AEV front bumper, HD rear bumper, rock sliders, skid plates and all of that is weight.
I put a roof rack on it and a RTT a couple of years ago and drove from VA to CO, several of the high mountain passes and all around. It was solid, ok fuel economy and could hold at 75 mph. The RTT was a fuel hog.
Off road it was a beast and never felt i needed a locker once (although that is in the plan eventually) The LSD was great and never let me down. Low 4wd it just crawled along. Imagine with a Rubicon transfer case.
I have 90k miles on mine, bought it with 45K.
Work done:
Had the oil cooler replaced at 80K (was leaking and a common issue)
Oil changes.
Things it needs now:
Brakes (they are due)
Clutch (teaching my 16 year old to drive is killing it)
Radiator (I can smell coolant so I think it may be going, been this way for a year)
Rear diff seal cover is weeping (easy fix).
That is it. I would drive it back out west again in a second.
Does it have squeaks and rattles? Yes and no. Yes if I put the internal Highlift mount in and the fridge, extra battery, underseat drawer etc. No if all of that is out.
Solid and reliable.
Do I miss my Fj60. No, while it was amazing and no issues with it at all, I needed to carry spares of what would be common items on the JK as they would not be available anywhere. Where everyone says smiles per gallon on the FJ, I get with the manual trans JK.