Your mechanical 8.3/Allison is one of the best combos they ever made. Like the above post, turn the exhaust brake off as that is what's probably defaulting the Allison to 2nd. I only turn the "mode" on in rolling hills as the change in shift points help there the most.
Your heat issue is probably the electric controller that controls the water flow. If you have a generator on a slide you can access it there and using a 9V battery see if you can get the motor to operate. The cheapest solution is to replace it with a manually controlled valve that you open in the winter and close in the summer. This will also help your AC in the summer as the electric controller is bad about not shutting all the hot water off.
Do not give up on this rig.
