I have a 2004 Mack roll off so where do I start this truck started having trouble building air it started at it would stay at 90 idle then 80 then 70 within 3 months so I replaced the air compressor and air dryer and governor and it wouldn’t build air past 50 idle or on the gas so I got another air compressor saying well maybe I got a bad one no it still won’t I bypassed the air dryer and nothing and bypassed the governor and still nothing this is my only truck I need help guys and it has 760k miles on it
