Thanks for reply.
I'll check the mounts as well, as I have to crawl under the truck to find the source of another broblem - whining noise is coming from the front at speed above 35 MPh. All driveshafts' rubber boots are OK, so I'm kinda hoping it can be one of the wheel bearings. Otherwise it has to be something really bad - front differential or even transmission. Any known common issues? This truck was used on a really soft beach this summer on a regular basis - at least once a week (I have to say it outpeformed brand new F-150 and Titan), so everything is possible.
Regarding the idling problem - I was told that I should try to replace camshaft position sensor as well and it may sollve the problem??? Like I mentiond before, it doesn't vibrate in a range 800-4000 RPM, also feels quite well while driving.