I have a 1993 M923A2. The air pressure relief valve (65 psa) to the brakes keeps releasing air on a periodic basis. I have just replaced the PPV valves with a Haldex L31258 (equivalent to a 90555396) with no change in the relive valve releasing air.. My primary and secondary dash gauges read at about 90 psi. Would I be correct in assuming that the problem is with my governor adjustment or a faulty governor. If is the governor what what would be a correct replacement number.