'95/older vehicles use OBD-I computers. Cant remember if that version throws a trouble code for EGR problems, but if you can borrow a hand held scanner tool it may detect one. I think the dashboard emissions light would also come on if it was EGR related?
Does that 1-ton van have an overdrive? Look on the end of the gear selector knob for a pushbutton. If it has O/D, does the tranny keep hunting for a gear when the motor stumbles, like its trying to compensate? Turn off O/D and see what happens.