I have had my Evo 8 for about 6 months and tracking has really been quite good until recently. I noticed about a month ago that the tracking was actually quite poor all of a sudden. My target (star, moon, sun) would often drift out of the FOV in a matter of seconds (5-30 seconds variably).
After scouring this forum I decided to update the firmware and I went to the latest version from HC 5.29.6226 and mount 7.13.7125 and, like magic, my tracking is dead on. I tested with Spica at 43 alt and Arcturus at 69 alt and it was perfect.
I am not sure if the firmware update fixed something or what but definitely something to consider if you are having problems.
So why did the problem develop in the first place? No clue except for the fact that I started doing solar viewing a month or two ago and that uses the solar tracking mode instead of sidereal so my only guess is that the mount was getting confused about which mode it should be in. But that is just a guess.
In any case, I hope this helps somebody and maybe avoids a needless shipment back to Celestron.