My problem is with a 92 4.3L sonoma 2wd.

Been chasing an intermittent stumbling problem for a long time. replaced wires, fuel filter, coil, distributor, map, sensor, and replaced the injector that was cutting out. but the brand new injector still cuts off and the stumbling starts. the truck barely runs because of the lack of fuel. the truck still drives, but has no power. it runs about 20 mph tops with the pedal to the floor. What would cause the injector to cut out like it's doing? could it be a bad ECM?

i've done some searches and found some possibilities. what do you guys think?