I have a similar concern as I have been on a steady Norco binge for the past month, taking between 2,800 and 4,000 mg APAP daily. Once I hit 4g/day I switched to CWE even though I'm taking a small (maybe insignificant) hit on the hydrocodone through quick extraction.
I am a worrisome individual and I instantly consider the worst case scenario when it comes to this stuff (which isn't a bad thing, I guess, in the spirit of harm reduction), but as I am asymptomatic right now, I think that the 4g prn daily limit seems to be pretty safe. I wouldn't be too concerned with doses under 3g/d. APAP OD at the acute level is something that requires immediate action, but at doses under 3g/d I would simply place a call to your GP and ask for a liver enzyme screen if you want to be 100% sure. If you've been staying at this level for more than a week, however, I really don't think you have anything to worry about.
That being said, if you develop symptoms that do not mimic opioid dose (yellowing of the skin/eyes, vomiting that doesn't relieve the nausea, pain in URQ (below the right ribcage that doesn't go away)), go get checked out. A few hours of your time is worth it and the doctors shouldn't shun you or treat you like a jerk if you tell them that you've been taking 3g/d APAP for pain, that's well below what the PDR considers acute or long-term OD.
Cheers
