Thanks, all, for your feedback.
Including Ed's humorous semi-snark. . .
Don't think tire pressure was a contributor, JLV has it set at 90 psi based on the front axle's weight & tire size.
Engine has the correct Vicker's pump for the higher pressure Sheppard box, he's not sure if the pressure relief valve is set correctly, so he's going to look into that.
Caster might be an issue, and was an excellent suggestion. JLV's going to call some local charter bus outfits to see who does their front-end alignment work and have it checked.
Again, thanks, all for your feedback, 'tis appreciated.
RJ & JLV