Press on the Gas and the truck dies

I have a 1991 Ford Bronco XLT 5.0. I've had the truck since i was 16 and
never had any problems out of it until recently. the truck has been sitting for a
few years, But I got it shipped to where I got stationed at recently and it drove
just fine on the 10-minute drive back home. I parked it and went to start it up
when I got up the next morning and it had trouble starting up, when I got it
started, I noticed when I press on the gas that it tries to die but as soon as I
let off the gas it goes back to idling. I replaced the fuel pump, fuel filter, and
spark plugs. none of those helped so now I'm trying figure out what the
problem is before i spend anymore unnecessary money. any advice would
help and be much appreciated.