Stopping blenders slow down for perfect looping

Hey! So I have been wanting to create a loop of something spinning, however when I rotate it 360° and play it back; it slows down near the end. Is there any way to fix/remove this?

In the graph editor, select the rotation channel keyframes, then press T and set the interpolation to Linear.
http://www.pasteall.org/pic/show.php?id=70201
To loop, press Shift+E then set the extrapolation to Linear.

Thank you! I have been struggling with this forever lol…