Thank you.390 milligrams is a lot of methadone, I really hope your being careful mixing that with depressants. Benzodiazepines blunt the the effects of ketamine. If I ever wanted to end a ketamine high short, I could achieve that with a low dose of diazepam.
Ketamine and opioids can be combined in medical practice, it's just not a combination with a particular synergy. If what you're looking for is a clean and potent ketamine experience, do it alone.