1990 ford f250 gasser help

[ford99PSD]

1990 4.9L inline 6 cyl. here is the problem. extremely fluxuating idle. from 250rpms-1000rpms just sittin there, even if it is warmed up already. first gear is strong, second it has no balls. it chugs down hard to where it seems like your flooding a carb.(this is EFI) same in third but above 3000rpms it makes a high pitch squeal but i cant find out what is making it because it doesnt happen in Neutral. any more info let me knwo. its my county truck and i need it up and going again.

[sldghamr]

have you done your maintence lately?? air filter, spark plugs, fuel filter.......