Engine Hump??

[Juantwo3]

OK, so my s13 coupe has been making this forward and backward shifting movment while between 2,000 and 3,000 rpm while i holding at a set speed. it does this in every gear EXCEPT when i have it in nuetrual. I changed the transmission mount it was obviously broken, but it continued to make the backward and forward motion i converted my auto to a 5speed about 3 months ago and i bought a used flywheel, so thinking to myself that maybe it was warped i replaced it with a brand new one along with a new excedy clutch kit (stock one). it still does it just not as bad as it used to. i googled it nothing came up.

any help would be greatly appreciated