On off throttle chain slack issues, possibly throttle cable ?!

[Tubz1983]

Ok so I fitted a brand new chain set (extra tooth on the front sprocket) and I've adjusted it a couple of times over the past few months, however recently I've really felt that slack feeling u get, like a chain whip almost, when on and off the throttle (almost seesaw like) obviously I figured it was the chain again, tightened it up to acceptable levels (not guitar string tight but not flappy either). I still have the same issue?!! Any ideas of it could be something else ?
Thanks as always
Toby