Turn signals will work sometimes then they stop

I'd start by substituting the flasher. They are no longer the cheap, common sense thermal units that worked fine forever. They are electronic assemblies now, and given the environment these delicate circuits live in, it's a wonder they work as well as they do. The electronic units commonly develop a number of different intermittent symptoms, but one clue is they almost always affect both directions the same way.

I don't know where the flasher is on your truck, but on the '96 and newer Caravans, they were plugged into the Body Computer in front of the pedals. That was a different design that was very heavy, and sometimes they would work intermittently because their weight and vehicle bouncing caused them to pull partially out of the socket.