Wow.....three inches of chain play? That's a lot! I found that if I didn't adjust the chain play to the midpoint of the spec I would get lurching at lower speeds.
Depending on your total miles, you may need a new chain AND new sprockets...at least tighten up the chain to spec first. (~ 1.2")
If you are going to buy a new chain, an O-ring chain is worth the extra $ many times over.