Name calling 5.5 year old - need help

My son has been on guanfacine for the last 13 months and that has helped alot with physical aggression (he used to hit me and dad and that has stopped since starting). I (mom) did PCIT with him from August-January and that stopped physical behaviors towards his 4 year old brother when implementing the time outs at home

Now, his name calling has spiked. Just this morning he called me a "stupid old woman" and has been calling me woman in a mean tone whenever he's mad. He calls his dad by his first name and will call younger brother "booty butt" and other potty names to upset him. The PCIT breaks arnt helping, telling him I'm sad when he uses those words doesn't work, early bedtime isn't stopping it. We only do screen time for a movie night on the weekends

Another thing that happened this morning, his brother went to work on a magnet tower that he started. 5 year old told him it's his tower then 5 year old kicked it down and blamed 4 year old for knocking it down. I told 5 year old that I saw he kicked it down and he said "stop old woman, no I didn't". I had him take a break for calling me old woman

Once he starts to get angry, it spirals. If the anger can be avoided, he is so sweet and loving. I'm heartbroken by how he treats me and the family when he's angry

He is in preK and the teachers have not been having issues with him. They said he will say poop words with friends but he is not the primary instigator of it

BLUF: How do I stop the lying and name calling? If you've been in this situation, did any of the impulsivity medication's work for you when added?