Heater problems sound exactly like I have experienced on my coach. That transmission problem I have not encountered.
On the transmission, I would first check the air shift valve on the side of the transmission. If it starts leaking your transmission will not shift properly. Also check the air pressure going to the transmission. It is the top pressure gauge and adjusted in the engine compartment, front wall, passengers side. The others will be system pressure and the adjustable tag axle pressure on the bottom. These are adjusted by lifting up on the cap and rotating it to increase or decrease the pressure. When you have it where you want it, push the cap back down so it will lock in place. Newell says that the top pressure (transmission) should be set at 60 psi. I agree that mine shifts more smoothly at 60 psi but I have to run mine at about 80 psi or my cruise control doesn't work properly (something that neither Newell nor Allison can explain since my cruise control runs off the DDEC). It might make sense on an earlier coach that used an air throttle rather than an electronic throttle. When I bought my coach, the Detroit/Allison service center said my transmission air valve was leaking and replaced it. I believe it is on the passenger side of the transmission and should have an air line running to it. May or may not be your problem but certainly something to check.
I have the same issue with my front furnace under the couch. I have held off on replacing it until the weather warms up enough that having the propane shut off to the rear furnace is not a problem. In your case, the fastest (and most expensive) option would be to replace the furnace with a new one. If I were on the way to Alaska, that is what I would do. It is likely the control board BUT it could be several other things, igniter, sail switch, gas valve, etc. I would feel much better heading to a cold location where service centers are few and far between with a furnace that I could depend on rather than 'hoping' that the problem was properly diagnosed and repaired.
Last, but no least, the dash heater. First question, how is your air flow at speed? If it is pretty lousy, first make sure that there is NOTHING blocking the return air grille under the passengers seat. 100% of the air coming out of the defrosters and the dash vents comes through that air grille into the heat exchanger. If the flow of air is adequate and the heat just isn't there, make sure that the supplemental water pump located on the driver's side of the engine compartment is operating when the temperature lever on the dash is moved to hot. It is a LONG run from the engine to the heat exchanger located in the passenger's side front compartment. Without the supplemental pump, there is even less water flow through that long line. At speed, the front of the heat exchanger is getting hit from that cold air coming under the front of the coach also. I have thought about constructing a air dam from the front cap back to the heat exchanger to block off some of that air but have not determined the feasibility of that option yet.
If you haven't, you might verify that all three blower motors are working. They are located in the passenger side front compartment ahead of the generator fan. Remove the four or so screws in the metal surround after you raise the access door, slide the side panel to the rear and remove it, then slide the rear insulation/backing panel straight out toward you. You will find three blower motors at the top of the compartment and the heat exchanger below the motors. The two motors closest are the dash/defrost blower motors, the third blower motor, located further back into the compartment, is for the arm vents. Make sure that they are all working on all three speeds.
I find that my dash heater/air vents blow somewhat better when the panel is off indicating a restriction in the air flow from the return grille.
Does your engine run at about 180-185 degrees in cold weather? If not, your engine thermostat may be defective. That would also reduce the amount of hot water that would reach the heat exchanger. You might also try to blow the dust out of the heat exchanger with pressurized air, don't get carried away and bend the fins on the exchanger.
If Newell owners of 1990 through early 1994 models have a large air flow out of their dash heater/air conditioner, I would like to know. I would also be interested to hear if any early 90's owners that have a dash heater that really heats well at speed.
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