04 4.4i tranny issue question

[AC2717]

Hi Guys, I was finally able to pin point when this probelm was happening.

X5 is already warmed up, and I am in motion, then lets say I turn onto another road or get onto the highway when I am already in motion. The only thins I cannot really tell is that it happens from either first to second or second to third.

the issue:
It holds the gear way too long and then slams into second or like above sometimes into third, if I take my foot of the gas it lessens the slam. It does not do it all the time, as in not every day, but it is getting more frequent.

We have reprogrammed already. My mechanic, a cert Indy shop was saying that was a vaccum system in the tranny or transfer case that might need to be replaced or something like that
who has expereinced this before? and what did you do
thanks