Nice 59 stovebolt 2355 what color is that paint? sounds like my rear brakes lock alot like yours on gravel and a few times on dry pavement so If I plan not to haul anything in it and just cruise around town I should adjust them as it is always going to be empty and light in the rear. The truck really stops fine just a couple of times in the last month the back brakes locked up so I thought maybe something was wrong but it really sounds like your brakes.
