1983 g20 Chevy van rough idle

Have a 1983 g20 I just bought, 104k original miles. Drove an hour home fine. Few days later filled up added some high mileage sea foam little less than 1/2 bottle.
10 minutes in. Engine is shaking and sputtering. Oil temp fluctuating.
Went to auto zone and grabbed new spark plugs and wires. No leak as far as I can tell oils and everything perfect.
Bought spark plugs and wires. Swapped them out. I noticed choke does not work and stays open. Wires are correct.
Did not use a torque wrench, tightened finger tight then until snug.
Took the van around the block and highway and was fine. Yet an hour later idle is rough soon as I step on the gas, a look at the jets and both are fine, used carb cleaner.
Pickup isn’t amazing on freeway but is there, just at stops engine will shake and die. Didn’t mess with idle screw or anything of that matter. Wasn’t sure if I need to grab a new coil or something else entirely.
Looked like the spark plugs where never changed, oils are all changed.
Bad gas? Something stuck in the carb?
When pulled off the dog house I noticed remnants of a rat yet would assume if anything was wrong that initial drive over an hour I would have known?
Any help greatly appreciated do not have the money to spend at mechanic at home doing it myself.
After new plugs and wires the oil gauge is at the first line and idles rough till dies, lights dim etc until I press the pedal. New battery.
Alternator? Coil? Carb? At wits end

Since no one has weighed in on this I will throw out a few wild guesses since it ran fine and then it did not.

Vacuum leak will cause a rough idle or dying at idle.

A debris particle has gotten into an idle circuit on the carburetor. This will not be seen by the naked eye.
Sometimes what will cure this is to remove the idle mixture screws (I’m assuming 2 and a 4 barrel carb), spray some aerosol carb cleaner into those screw holes, and then blast the holes with compressed air. It MIGHT work without compressed air but a bit of force helps.
Back in the day when I worked with some carburetors I cured a few carbs of rough idle problems with this method.

Looking at it right now, definitely think some particles got into it, as with new plugs wires coils, battery and alternator are good.
Runs great on the freeway thus I’m not sure if it’s a vacuum leak,
Will look at the idle screws etc

If the vacuum leak is due to straight manifold vacuum it will not be noticeable at speed. If a leak is ported vacuum (meaning above the throttle plate) then any symptoms may be surging or even bucking.

A straight manifold leak will only be noticeable at idle either with a stumble or flat dying; depending upon the size of the leak. This would generally apply to carbureted models as once the car is at speed on the road the idle circuit in the carburetor becomes a non-factor and it’s just along for the ride.

Possibly the EGR valve is leaking. Is there a Check Engine Light on the truck? If so an electronically controlled carburetor is likely and they can be tough to deal with.