I'm hoping no shop would put E-rated tires on a wheel that isn't rated for the maximum PSI of the tire, but that's certainly worth looking into. Unfortunately, most such numbers are on the wheel rim UNDER the tire and one has to demount to see them. If the wheels are factory, Ford should be able to answer that question, though.
For PSI when towing, most go with axle load/weight. Since you have your axle weights, you might look at an inflation chart and go from there.
Here's one such chart- it's not from Michelin, though I'm not sure it matters- size/lr's are pretty standard throughout the industry.
Note:
Numbers given are per tire.

Chart from
this link