Alright so i noticed this a while back that while driving in 5th gear my rpms fluctuate between 100-200 RPMs while just cruising. I felt it and it got me a little curious and then i finally replaced my cluster to one with a tach and it confirmed it. This only happens in 5th gear with partial throttle cruising at 2k RPMs it will just start to go up and down between 2-2.2 and it is a weird sensation when it does so. Any thoughts on what is going on? Keep in mind it only does it in 5th not 4th or below and at 2000-2200 rpms not higher or lower.

Did u find anything out about the problem?