Is my furnace working correctly?

I had similar heat distribution problems with my fifth wheel. When I opened up the basement to have a look, I discovered that the techs at the factory had installed the ducting as though they were in a hurry. The seams weren't sealed, most of the hoses were partially or fully disconnected, the tape had come off of about half the joints.... it was a mess. The pipe connecting the furnace to all the vents in the living/dining area wasn't attached at all. I did some quick field repairs (which made an 80% improvement), but I need to pull the coroplast off of the entire basement and go over the ducting with a fine-toothed comb during the off-season.

You may have similar "built on a Friday afternoon" issues with your rig.