When cold, the van starts right up and runs fine, but when it warms up after a few miles it begins to buck and jerk and lose power to the point where it will barely get above 20mph. Eventually it dies and won’t fire up until it cools off a while. No ‘check engine’ lights or warnings of any kind. Any ideas about what’s going on?
Does the engine warm up quickly and reach the correct operating temperature?
I would start with ignition components (although it says “update” so maybe some activity was already reported there). As electrical stuff gets hot, resistance increases and all of the electrical flow has a harder time getting around. Plugs, wires, coil…whatever the components are. If you have an ohm meter you can test according to specs (you might be able to find the specs in the online Autozone repair manual - www.autozone.com).
From those electrical parts I would move to others, such as fuel injector wiring and such.
A failing fuel pump could cause this. How often is the fuel filter changed?