4th gear RPM drop (AT)
 

Its been doing this for as far back as I can remember. Every time the car shifts into 4th gear, in either M or D after about 1 second in the gear at constant peddle pressure the RPMs will drop about 15% of the rev range from wherever you are for about a half second then go back to where it was before the drop and keep climbing like it should have. It is incredibly noticable in the higher rev ranges obviously as it can drop like 500rpm or more. Driving fairly normal (shifts in the low to mid 2000s) its less noticeable when its like a 100rpm drop. Its always there though no avoiding it. Does anyone have any idea what could be causing this so I can go to the dealer with a little more knowledge. thanks

Happens to me too, from what I was told its merely the TQ converter locking in, I've gotten used to it and even utilize it when accelerating. If you add a bit of pressure around the time it usually happens you can lock it quicker, so fast its barely noticeable.

Is there nothing that can be done about it? And why would it only be in that gear?

Mine does this in second gear. It can be annoying at times...

Happens in all gears, its just more noticeable in 4th. Why does it happen? Its the torque converter locking in.... If you're unfamiliar with how this works this post is very helpful: http://xtremecarzone.com.au/index.php?showtopic=939

You can also check the 'how stuff works' it's really dumbed down but its pretty helpful if you're unaware.

This happens to me most notably in a 2nd to 3rd shift, and usually only if I'm in M mode.

No chance this is just a lousy execution of rev matching?