My 1990 Gmc Sierra is possessed

my truck after it warms up completely cuts out at low speeds like when idling through a parking lot. The lights flicker and the truck will die it cranks right back up but will continue to do this. I have tried The IACV on the tbi, spark plugs and wires, fuel filter please help

Have you tried looking for vacuum leaks?

yes and no vacuum leaks were found My mechanic is even stumped.