Agree with all the above .
hoping that one of the items replaced was the cause and you don't see any more symptoms .
also , the PCM used on 1996 and later Cherokee , grand Cherokee and Wrangler with the three angle plug harness design is prone to problems and noted for it . The internal connectors loosen where they are soldered to the printed curcuit boards . Whether that be due vibration or excessive pressure upon disconnecting and reconnecting , that has always been a question .
as far as the serpentine belt , yes , take a good look at the tension it currently has on it .
granted , you've got a new belt and tensioner installed . Replacement parts quality always seems to be questionable at time . But the tensioner may not be the cause . First take look at how the belt is routed on all pulleys in the event that removal has been decided . Many have been through this . The sticker under the hood is missing and no one has a proper diagram for that engine and more in particular , that model year . Make your own diagram . Save your own sanity .
i suggest the belt be removed and inspect the belt carefully . I realize it's new but there is a problem . if the belt shows any signs of damage , inspection of all the pullys and accessories the belt drives will be necessary . Been through this on my dads 99' GC 4.7 liter . In his case , it was an alternator pully with some rough splines damaging the belt .
Not only will you need to examine the spline surfaces AND the smooth surfaces where the back of the belt rides ( I.E. , water pumps ) bit you want to be sure the accessory itself isn't causing drag . Most of the time this occurs in my experience , it's either a tensioner , a pully or an accessory.
by accessories , I mean alternators , powers steering pumps , a/c compressors , water pumps or on earlier vehicles , emissions pumps . Any belt drive item that has drag or the potential to momentarily lock up can and will cause this " squealing " to happen . Loose belts can cause this too so we must be sure as SuperJ posted to check our belt tension .
So , first check belt tension as it is in its current assembly . Run it if you'd like .
check the belt surfaces next . It's best to remove the belt since it's difficult to see the entire belt while on the engine . It's a new belt so any damage will be seen immediately .
next , roll all accessory pullys and note their movement . Do they drag , wobble , visible damage , etc. . Just because a belt and tensioner was replaced , dosen't mean there wasn't more to fix.