Is it my Vacuum system ?

[Austin85]

1982 W123 - a 200 euro saloon model
I have been having issues with acceleration to full power ( 109hp gasser)
literally had to downshift to 3rd gear to hit in the 30mph range. 4th is maybe topping out at 50mph on flat highway roads only.
I am thinking or hoping this can be a vacuum leak issue somewhere.
Other issues that popped up recently are my brake pedal out of nowhere got soft and my trunk lock stopped working. edit * my door locks sometimes open and other times not.
I'm in a small town in Northern Colombia and they do not know these cars here very well.
Recently installed new plugs, ignition wire set, distributor cap and had my tank filter cleaned. I was told it had some rust clogging it. Hoped that was my solution but here on day 2 i just had all of these issues pop up.
Please offer suggestions ..Is the vac system related to brakes and acceleration in any way? Thanks!