hi, new to the thread & need a little help w the bosss van n the heat.changed the thermostat &the heat went down hill.cganged the heater core & the same low heat.heat gets warm when you go up hill or into the gas & takes longer to get any heat at all.heard bleeding it through the 2 bleeders in the front of the engine, did it 3 times,aahhh.now rear heater blows cool.so stumped scratching my head.got some air out but aahhh.any help would be so appreciated.