Hate this blazer

Have 98 blazer LT, brakes started getting spongy and losing pedal. Checked for leaks and found none but noticed air sound from booster was louder than normal. Changed booster and tried bleeding brakes but could get little fluid to right rear caliper off the bat. Same with the rest, also brake pedal is extremely high. Read about adjusting push rod on booster but was kinda unclear. Any advice on this would be appreciated. Forgot to ask if anyone thinks proportioning valve could be causing this and how to test it.