I would echo much of what Buzz has said. I had horrible side effects from my initial 2016 starting dose of 300 MB 2x/day Tasigna, including 40 - 50 squamous cell skin cancers in a 4 month period, terribly swollen salivary glands, mouth sores, dry mouth, fatigue, intermittent GI problems, headaches, tinnitus, muscle cramps, irregular heartbeat, etc. I was miserable and so I started lobbying my onc for dose reduction as soon as I hit MMR, which occurred in just under 90 days. At 6 months, he finally relented and allowed me to reduce to 450 mg per day, but insisted on testing every 6 weeks. Over the next 6 months, we did 2 more dose reductions, first to 300 mg/day then to 150 mg per day. Most of the side effects were gone by the time we got to 300 mg per day. During this period, my PCR also dropped from .1% to undetectable. Unfortunately, the irregular heartbeat continued and I started to develop peripheral neuropathy symptoms. I asked my onc to approve a switch to 20 mg/day Sprycel, but he wouldn't permit it, so last summer I attempted TFR, but with the explicit understanding that if I failed, I could restart at 150 mg and not full dose. My onc agreed but we set the failure bar as any PCR worse that .01% rather than .1%. In 75 days, I hit .02% and restarted 150 mg/day Tasigna.
About 3 months later, I finally convinced my onc to allow me to try 20 mg Sprycel and I have now been on that for nearly 6 months and just reached undetectable again last week. I have little to no side effects so I feel that this is more tolerable for now than Tasigna.
I believe with all my heart that dose reduction should be started once a patient achieves and maintains MMR for 2 consecutive 3 month tests. The goal should be the lowest possible dose while still maintaining MMR. In your case, you have far surpassed MMR and you need to lobby your onc hard for dose reduction. If unsuccessful, find an onc who will allow this. The money saved by lower dose more than pays for the extra testing. Sign a liability waiver if you have to, but you are long overdue for dose reduction and then possible TFR.