The past week I've noticed that while in 4th gear at a high speed of say 50 mph or more that my rpms will go up 500 or so without any effect on the speed. I have to carefully keep the gas pushed to the right spot so it doesn't occur. Its when I attempt to accelerate more in a sense.

Am I looking at a bad clutch. My OD on M46 works when cold but not after warming up. (I've got the rebuild kit waiting) Can the OD on a manual trans effect the 4th gear even when its not engaged? When I attempt engage the OD I sometimes sense that its slipping in and out. Meaning I have the light on but my rpms are at 3000 @ 65mph and if I let up on the gas the rpm's drop to 2500 quickly unrelated to speed. I can't be sure if this happens without the light on but I'm pretty certain that its only with the light on unless I'm climbing a hill.

Should I be looking at the clutch or OD or both?

Thanks