1998 Jeep Laredo whining noise from rear end at 40mph

Did you replace the carrier bearings too? Another thing to check is the transfercase, when these whine, a lot of times it will sound like it is coming from the rear or the front. Are you running all 4 tires the same size, if not, this could be your problem too as it will create a binding and wear out your axles, transfer case and other stuff too. LEt us know how you fare and if you need further help.