does your 4.0 do this

Had my xj for about 10 months and im still learning. My 98 4.0's oil press. sits at about 40 when driving steady, after its been driven a while the idle pressure runs around the first hash mark or a little above, but it stutters and never really settles down. Also after a drive if i shut it down to open the garage and then start it back up to move in once it catches there is this llittle knock for a second. Tell me im paranoid and/or its a jeep thing and live with it. Id hate to have to replace main bearings alread ( its got 113k on it) Thanks much!

It sounds like your 4.0 is behaving normally. The oil pressures are fine and that little "knock" that you're getting upon start up is probably coming from the lifters for that split second before they pump up under oil pressure.
Just relax and enjoy the performance.

The factory gauge isn't 100% accurate, but okay for a guide. The specified oil pressure is 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. It sounds like you are in spec.

MY 98 4L sport does exactly the same thing, the second day i got it.... (got it 10months ago like you) i freaked out and drove it straight to the mechanic and he said everything is fine! good luck...