Krank,
I've been on methadone for about 20 years, started at 19-15 mgs./ day, 2nd accident, went up to 100 mgs. titrated down to 50-60, which is where I am now.
I have never had any side effect such as mood swings, other than constipation, which a bit of miralax otc, works fine for.
AS someone else said, your mood swings are from all the anxiety that comes with pain, and life. You may want to consider speaking to your doctor about Cymbalta. It is an anti -depreessant, that also has been found to help with nerve pain! I take 60 mgs of that /day.
Also, in day to day relationships, remember that perchance if your wife is in a 'mood', she's going to see you as a 'mirror', as we all tend to reflect some moods to one another. All you can do is make a conscious effort to be 'happy'! I suggest it!

Be well!

Pete
asb