Advice on GM 2.0T weird boost scenario

[dekes1]

Moderators: Posted to wrong thread. Please move to GM I4 Engine thread. Thanks!

I have a confusing scenario that I'm hoping someone can suggest a place to start.

Caddy ATS 2.0T w/ automatic. At a highway speed of about 60, when i pin the throttle, it will downshift into 4th and the revs will climb normally. Boost shows a start of 14psi and tapers off to about 11 at redline. Then, it'll shift into 5th and once again revs climb normally. BUT, boost shows a constant 18-19psi all the way. Why would the first climb in 4th gear only allow 11-14psi but as soon as it shifts into 5th it allows 18-19psi? Stated another way, why am I not getting 18-19psi in the first climb?

For the record, in a normal full throttle run from a dig, it will stay at 18-19psi in all gears (including 4th) so this behavior only happens when i floor it at speed and let it downshift itself.

Any have suggestions on parameters I should look at to experiment with? Thanks guys