Problems with Furnace

Hi,
I am having issues with my furnace. I have look all over the internet trying to figure it out with no luck. The area I am in has no mobile RV repair men so I am on my own.

The furnace is a Atwood Hydro Flame 8900-III model 2540. This is in a 2010 HitchHicker.

The issue I am having is the heater will blow warm air out of the 2 living room vents, but it the rest of the vents in the camper it blows slightly warmed air. I do not believe any of the vents are blowing as warm or hard as they should be. Also the furnace fan seems to be louder than what it should be. It has kind of a vibration type noise. The heater seems to be working correctly besides the noise and lack of heat.

I have checked the propane buy turning the stove, furnace, and water heater all on at the same time. I could not tell a difference in the burners on the stove. I read to check that online. I checked the battery voltage while the heater was running, and the voltage held pretty constant at 13.5. I also checked and the squirrel cage fan blades and they are clean.

I appreciate any and all help and advice!

Thanks,
Welder85