Need some help

Hello all I in need of some help I pick up a 89 R3500 it has the 454tbi th400 when I got the truck. It ran ok but the temp never went up and at low speed the heat worked but over 45 just blow cold. So I checked the thermostat it was stuck open so I replaced it now when I start the truck it has a high idle and when worm go to put it in gear. It dies on me I have replaced the map sensor and the injectors look like they are spraying way to much fuel. Any help would be great

Replace the coolant temperature sensor. Not the one-wire one on the head that is for the dash gauge, but the two-wire one on the intake by the thermostat. It tells the ECM what the coolant temp is. They fail in a way that reads colder than actual temp and cause over-fueling.

Richard