VNL 860 very occasionally free revs in gear

2023 860 with around 125k miles. Always have stuck to the maintenance schedule. Truck will very occasionally free rev in gear right when it tries to shift. Air pressure doesn't seem to be a factor. No codes or CEL on the dash. Seems completely random. Has only done it maybe 5 times total. Once rpms drop enough it catches the gear.

Anyone have any ideas? Local dealer is new and full of ####ty techs.