I have debated responding to this, because my response will show that Rush could be capable of functioning while abusing Pain-Killers. So I will caveat it with the fact that I think the Cline's are lying through their teeth to make some money. I think in the end we will find that Rush is clean, or at the worst borrowed a couple pills a time or two when his ran out.
But back to your question " You know one that has me bugged about all of this that I haven't seen anyone mentioning? Just how does one play a pretty decent 18 holes of golf while being this strung out on painkillers?" -- the same way that Brett favre could win the NFL MVP and lead his team to the Super Bowl while strung out on Painkillers (Vicodin).