alternator belt FROM HELL !

hi guys , since my friend changed my alternator , my belt screams like crazy in the morning when the engine is cold and even gives the tranny a hard time to shift for second speed , its scream as hard as the exhaust ! my belt looks loose , but it always ran since the last 6 years like that..and never screamed before we changed for the new alternator .... can it be too tightened or too loose ? or even can it be the pulley ? , since the last few days im putting a stuff to lubricate the belt , that i bought at canadian tire , work wells when i put it 5 minutes before heating it up in the morning but still, once i stop the car it will do it again , and its always , always at low speed, and the the engine is not heated up ..

your advices ? thx !

Joe