I've had them on my truck for over 2 years and I haven't had a single problem with them yet. The hardest part about the installation is removing the stock mounts. The best part about them is if you ever need to replace the bushings (high unlikely), it's only like $10 for all four of them. Might want to hit them with the rattle can or get them powdercoated.
I just got mine done, its the first 4.0L motor-mounts he's made and I lent him my truck for a couple of weeks so he can do the development on them. I love it! A little more vibration now since they don't allow the motor to move as much but that is ok. The 4.0L stock-wise does flop around alot and with the OEM vibration damper I didn't notice it as much.
All-in-all, a good investment!! Can go wrong with Autofab's motor mounts!!
the mounts are very nice, not sure how difficult to install with the engine in the chassis, the set i helped on were easy without the engine. take a look under your truck, all the rivets that hold the current brakets to the frame need to be removed, some could be difficult.