High idle speed after warm-up

Hi there, long time here without posting but I have come across a new question I'd like to ask. Tried looking through the archives, and apologies in advance if I'm asking something that's already been gone over. I drive a 2018 TRD Off-Road, auto transmission, V6, since I bought it in early 2018. New issue for past few months seems to be that it's idling just a tad too high when I'm stopped at a light, with transmission in 'drive'. Maybe right around 600 rpm is what I'm seeing on the tach at that point? But when I shift into neutral, rpm quickly bumps itself up only maybe 50 rpm, but that seems to be enough to get it idling more smoothly. This never used to be an issue with my truck. One thing to mention is that I had an aftermarket cat-back exhaust put on, but it was a couple months AFTER that was installed before I noticed any change in idle vibration while at a stop. Still felt like it's worth mentioning though. I also only notice this after truck is warmed up, since idle speed does seem to be higher when engine is still cold. Is this something that could be adjusted manually like on old cars, or is this an issue that's more involved than that? Thanks in advance,

 

If anything your idle speed appears low, at least compared to my 2020 v6 auto. Idle speed should be higher when the engine is cold...mine runs around 1300 rpm initially when temps below freezing then goes to 1100 after a few seconds.