I have a 97 3800 SC GTP. When driving it occasionally will slip out of 4th gear. Barely noticable if not for the Tach. Doing about 70+ at about 21-2200 rpm's it will jump to about 3000 rpms. Does not always occur but does occurs when everything is warmed up. Any suggestions on what this COULD BE? I searched the forum found alot about not going into 4th. Not anything like this.