yeah. make sure the one you get is for a setup like yours. the main differnce is in TBI and MPFI like ghost here is advising.
as to the carb idea: seems all the reasons against it have already been spelled out. you wouldn't need to necessarily change the intake manifold but you'd have to fins a carb that'd fit the "seat." fuel pump pressure would probably one of the main things you'd have to deal with besides the ECU starving for input. i'm sure it's doable but i can't recall anyone doing it.
rich condition: one of your sensors or the ECU are reading something wrong or not reading.. seems like you checked most of them. your timing is correct?
did the truck always do this since you've owned it? if not, when did it happen? did you service anything about that time?