Ethanol is hydroscopic, It absorbs water.
Heet is ethanol or some other hydroscopic alcohol, I am surprised they even able to sell it anymore with all the ethanol we get at each fill up.
"Seemed to help" is the power of suggestion, as all it did was increase the alcohol/gasoline ratio.
Ethanol is very hard on rubber fuel lines not designed for it, they can collapse internally.
Plastic fuel tanks are not happy with ethanol. Pretty much nothing is happy with ethanol except the corn lobby. Boaters despise ethanol.
I've no idea if another fuel system cleaner would help. If your van is Fuel injected, there could be micro fine screens on the injectors themselves which can be cleaned. They might have gotten plugged up from the high concentration of ethanol loosening gunk in the fuel lines. If carb'd, isn't there another filter right before the carb? That concentration of ethanol in the fuel tank could loosened up some gunk varnish in the tank itself and it could be plugging the filter sock at the bottom of the tank on the fuel pump module, if fuel injected.
Lots of could be's. Hope you find which one it is, or it sorts itself out with time.
If fuel injected, try disconnecting the battery for a while to reset the computer, it coulda learned some bad habits with 110 octane in there for a few hundred miles.
Not sure about Chevy, but I think your year is throttle body injected. If so it is pretty easy to pull and clean the the gunk/varnish from micro fine screens on the fuel injectors.
If you do want to try another fuel system cleaner, use one without alcohol in it. Seafoam is something like 40% isopropyl alcohol. Use techron, or gumout regane( has to say regane) or redline SL-1. These among some others, have PEA, poly ether amines, which are proven to clean and not leave deposits of their own when burned. These are said to be most effective when short trip driving, as opposed to highway driving. The heat cycling helps break up the carbon in the combustion chamber.