Stimpack is a turn-action if you're actively being attacked, though it's not delayed. Aimed Shooting, however, is not only a turn-action but also is the last thing that happens in the round, excluding certain other actions that haven't yet become relevant or I'm simply not allowing you to perform while in a potential combat situation.
Distance is usually a non-factor when it's just one living opponent, though for these melee creatures I still have to track it in some fashion. Since you haven't moved since your attack, you're still right were you were, and Grunt #1 is still right where he was - within range for a good hit with the chainsaw.
While I'm thinking about it, the Chainsaw officially deals damage at the same rate that an imp's claws do: 1d8+3. They have a slight bonus to hit (+1 both for and against anyone wielding a chainsaw, which I'll have to update the table to reflect that), and instead of increased damage on a critical, a chainsaw is guaranteed to hit any targets that fumbled before the attack (so, say you rolled a 1 on your attack roll with the shotgun blast...)
As for those fleeing Helltouched, I (a) completely forgot about the fleeing mechanic since that encounter, and (b) pretty much tacked those two guys onto the next level once they fled.
