I have no idea if anyone has ever changed anything in this truck. I would say that it is all stock.
The truck has 89k original miles on it and i got it from the second owner.
I dont think it was buzzing at 4000 rpm, but i dont have a tach...The truck wasnt struggling either it seemed real happy at 70.
The tranny is just a 4 speed [1st-granny] so I dont know about what the gearing might be.
Maybe I will go get a tach today.