Sorry you've had some problems on your maiden voyage!
You might be on the right track regarding the pinion angle etc.
It's a process of elimination as I'm sure you know,make sure the tires are not flat spotted from possibly sitting underinflated for so long,sidewall condition etc.
They may well be 'out of round' or starting to break down through age/dry rotting etc.
Jack the truck up and spin the wheels,they'll soon show if there's a problem..
Good luck.
