We have a diagnosis for the van. Good news - Bob was kind enough to do the diagnostic test for free!
More good news - it looks like we just need to replace the spark plugs and wires. (At least, we will start there and see...) Bob also recommended that we regularly use fuel injector cleaner, which we stopped doing months ago when the cost became a "luxury."
Paul will have no trouble changing plugs and wires himself. (Only cylinder number 1 is misfiring, so he may just replace that one. Because we cannot afford all six plugs and wires) Looks like we may still be able to make our trip to IL next weekend to see family.