[prairieschooner]

Jimmy,
We had to "learn how to drive" when we took our first trip. What I found out was that we could climb just about any grade (even with the car in tow) by simply gearing down, thanks Larry Bell. What I want to do is keep the RPM around 1800-2000 with our V-6 (6V92) and sometimes this means climbing the grade at 25-30 MPH. The good part about that is that I am at the right speed to go down the grade when we get to the top.
Yes the Coolant can make a big difference---what ratio of Coolant to Water did you go with? Some Hot Rodders will run only around 25% Coolant in the Summer just to help cooling, you need to correct this when it starts to get cold! Remember to use a Coolant that is compatible to your Engine and Distilled Water.
The Radiator needs to be cleaned every so often on our older coaches. I use Simple Green and spray a heavy concentration from the Engine Side, allow it to sit for a while then spray the Water from the outside of the Coach towards the Engine so that I push the gunk back the way that it came in.
You are correct about the Pressure --- Good Find! I have found that our Radiator may look low when cold but after it heats up the level should be in the Sight Glass. This was another "learning curve" when we went to Creed I over-filled our radiator and the V-6 burped it out.
I have since learned much about our Prairie Schooner.