So you're being told the mileage is accurate on your truck at 37,***??? How do we know that speedo has never been replaced? BUT, if it's not been swapped, as straight as those digits are lined up, I could sure see why someone seems to think it's original miles. Normally when you roll an odo, the center digit is not 100% lined up with the other digits. It could be either a little to high or a little to low. Also depends on the make of vehicle too. I've been told on some Dodges, that when the odo rolled it scratched one of digits as it rolled. It has like a thin line through the digits on 1 column. Also, spacing between digits can be off on some breeds.
@RetroC10Sport may know more about it, or even have some CarFax info on your VIN. If you see a repair or recall repaird at says 45,000 then you obviously know the odo isn't accurate. Titles usually can give some clue too if it's changed hands a few times along the way.