chocotacoking

hello. i am new here. i recently purchased a 1986 ford bronco II. in first gear, towards the end it will bog down, and struggle to stay running and then it will go fine. then i put it in second gear and it will do the same thing then it will speed up and be fine through the rest of the gears. also, the moto has to idle high for it to stay running if not it will threten to die. thank you and please help me.