Look at your truck door's lower hinge. There is a 'roller' and a spring. The spring puts pressure on the roller as it rolls across a bar with two bumps in it. The roller has a bushing ..but it is also under a fair amount of spring pressure. More than likely the bushing on your roller is worn (does it seem 'loose' on it's shaft?). When it does that it removes a bit of the spring pressure that would otherwise 'catch' in the valleys of that bar with bumps on it.
It could also be the spring is missing/fell out, or the bar with bumps is worn, or the hinge bushings themselves are worn (causing the two halves of the hinge to 'push out' ..again less pressure on that 'bar'. To check for a worn door hinge, grab the back/bottom of the door and pull 'up and 'out' on it ...up/down hard. If you feel movement, check the hinge bushings.
The fix is to replace the lower hinge assembly. If it's just a worn roller bushing, and you're the DIY crafty sort, a guy could compress and remove the spring (they make an inexpensive tool for that), and make or source a new bushing for that if you have a lathe or similar tool.