the air system is designed to drop the high side first, then drop the high end.
if not enough chassis air is left to raise the low side, the compressor adds air. if you have a small compressor, it takes a long time.
the excess slope light may be indcicating you are in a no level situation.
the leveling system is limited by the height of the air bags. if you have 6 inch air bags, you have essentially 4 to 5 inches of real leveling capacity. there is a bumper inside the air bag that doesnt allow it ti completely collapse.
download a service manual for your system. it should be either a 500 with a 14 inch control box, or 600 with an aluminum box about 6x x8 x3, it may be a double box depending on your model.
the 14x 9x 4 inch box on the 500 system is normally located in the ceiling of a compartment. the 600 system box is located normally under the dash. someone with a similar coach would know more about the location.
do the diagnostics. that should tell you what the problem is. there is a good section on the compressor. if the compressor is coming on, check the water seperator bowl for cracks.