If your headlights are working correctly now and you have both highbeams on at the same time, then you problem lies in the wiring at the headlights. Many conversion kits come with an adapter pigtail that allows you to plug your new headlights into your factory wiring harness. If yours was a direct plug in, the problem remains the same.
You have the wires for the lowbeam at the lights connected to the highbeam circuit of the coach. If your new bulbs are those with the high/low beams in a single bulb, there will be three wires at each connector, one for high beam (which also turns on the indicator on the dash) one for low beam, and one for a ground. The ground is usually a black wire, and will not need to be moved. You need to swap the other two wires around, this can be done either at the factory plug or the pigtail supplied with the conversion. It is probably better to do it at the pigtail and retain the factory wiring stock. If yours is a direct plug then someone has already swapped them once before. Depending on the type of connector you will need a special tool to depress the locking tab integral with the metal connector. You usually insert the tool from the back of the plastic housing Some though are inserted from the front (GM metripac type)until the tab is depressed and then pull the wire with the connector attached out. Bend the tab back to its original position before inserting the wire into the correct position. Hope this helps.