Engine power / braking force

Hello.

I need your help on the following subject:

V8, 3.6 (PT), Bj. 91, Autom.

Sometimes I realize that my wife. has more power
and is much better at gas. The running culture at higher speeds is also significantly better. It's strange.
the braking effect is better, i.e. I have to exert a much lower pedal pressure for a certain braking force.
As I said, the condition described above only occurs. Does anyone know this "problem"? There may be a vacuum line in the system somewhere, which is switched via a valve only in a certain driving cycle and this line, if necessary. is leaking and can draw false air?
I am grateful for any help!

Welcome

Guido