@vixb, you might consider examining, through self reflection via journaling or even revisiting therapy, why you might have this pattern of holding on to anger over, for example, driving incidents. After all, it's completely normal to get pissed off in the moment at other drivers when they do idiotic things, right? I curse at other drivers all the time, living in a congested urban area. And then I'm done, it's gone from my brain. However, I was married to someone who held on to his rage all day, then he would come home and vent to me in agonizing detail about some incident where he was cut off in traffic, or about some poor store clerk who wasn't nice enough to him in the checkout line. As if he was a special victim of their poor behavior. I put up with this for 23 years, then I was done.
You've described how you rationally trained yourself to control your road rage, but also that it's still there, eating away at you. So I think a legitimate question is, WHY does anger continue to eat away at you and get in the way of your emotional well-being?
Dont get me wrong - dealing with individual rage incidents through writing exercises is incredibly therapeutic (I'm a huge fan of the Unsent Letter myself). But the habit of holding on to rage indicates that there's something deeper going on. Rage is connected to feeling invalidated, and that's what needs to be examined from a much deeper, past point of view. Because, as Dr Sarno and Dr Mate both agree, it all goes back to childhood and family dynamics, usually because as children we were not allowed to safely express our anger and be accepted for what should be normal and short-lived responses over life's barrage of small frustrations and injustices.
I'm thinking that for you, it would be worth the time and the emotional effort to get to the bottom of this. You've done IFS, is there something in IFS theory which can see your rage from your point of view as a small child?