Important question. I just recently got a tj and am a bit confused if its driving properly. When i hit fifth gear and im going 55 to 60 the jeep is going over 2000 rpm. Is it supposed to be so high? or is it supposed to be like 1700 rpms at that speed. When i stopped at one light I could hear the engine accelerating by itself. Your help is greatly appreciated.
thanks  

i understand that some peoples jeeps will run at 3000 rpm. mine runs at 1900 rpm at 65 mph. alot depends on your gearing in the axles and tire size.  

Mine probably runs around that I just don't usually go that speed.  At 70 mph mine runs around 2500 rpm.  I have a tj with a 5 speed manual running 31's on 3.73 gears.

Now your engine shouldn't be accelerating by itself at a red light.  I am sure that you checked but are you sure your foot was not accidently on the gas pedal at all while it was on the brake.  If it wasn't then you might check to see if your linkages need a little lube to start off with.  

With the AX-15, your 5th gear ratio is .79:1.  At 55 you should be running 1750 RPM and at 60, 1916 RPM.  With 4.10's, you'd be running 1931 RPM and 2106 respectively. If I were you, I'd double check the gearing.  If it was changed, there lies the answer.  Also if it was changed and someone put a new speedo gear in, your speedo will be off, even in repect to the RPM calculations.
I have seen a gear swap in axles, but for some strange reason, when the cover was put on, they kept the origional tags stating the origional gear ratio. Very misleading!!!
On the engine revving thing. When you are slowing down w/ the clutch in, the engine will run at high idle (roughly 1000 to 1100 RPM).  It will only come down to low idle when you are at a full stop.
If it is running above 800 or so when stopped, check for intake/vacuum leaks or the idle control motor which is on the side of the throttle body.  

Oh, btw, those RPM's were calculated w/ 31" tires. If you have stock 29" tires, expect roughly 150 RPM higher.