We all know that in 2.3 they removed most elites.
In Arathi Highlands there are 4 mobs that wonder the whole instance;
Fozruk [level 42]
Sleeby [level 40]
Freeboz [Level 39]
Znort [Level 39]
Their spawn point is around 65.27 by Circle of East Binding.
The second you kill them, they respawn. Im not sure how much EXP you'd recieve per, considering I was on my level 70 when I spotted them.
The only problem I see with this is if you get behind, they start their pathing. So being higher level than them, twinked out, or being potted up with be recommended.
Keep in mind you may have to wander from Circle to circle to find them. Unless you feel like waiting up at their spawn point for them to path to the nearest Circle which is basically right there.
A hint that may be worthy to try: Try and just kill the little guys and leave the giant alone if your lower level. This might just make it so the little guys are the only things that would spawn instantly up at 65.27 instead of the giant aswell.
Good luck, enjoy the leveling.