Help! Hot Water Boiler. Split Level upstairs 4 degrees colder than main level, all pipes gurgle

Issues:

-upstairs (which is also the split level portion) is 4 degrees colder than main level.

-Can hear water running/gurgling throughout the house whenever the boiler is running

I have bleed every radiator multiple times.

House:

1950's 1500 sq ft split level.

-new boiler installed this fall (2024)

-set to 180F

-pressure is 12lbs

-will lose pressure if the supply water is shutoff

-Seems to be a single loop system, no zones.

-baseboard radiators along the 2 longer sides of the basement ceiling

-one baseboard radiator in each room above the basement

-I cannot locate any steams vents on the main piping

-air vent was installed at the boiler

Pictures are of the basement only