PPE, the S/C belt is tight with OEM length ,but when you rev it up over 2500 she'll start to slip and squeak.
OEM belt # 4060663
3.4 pulley # 4060658 by Gatorback or keep the oem belt and use larger tensioner pulley
BTW no need to re program ECM, ( I did not need it ,said the guy who re my ECM)