poulan pro lawn tractor has deck belt vibrations

I have a poulan pro only 1 year old , I have bad deck belt vibrations , I have installed new blades and a new deck belt still bad belt vibrations, it a poulan pro 19hp 42 '' deck from home depot any help would be nice

Check each blade , there should be no up & down or rocking motion.
If there is any movement the bearings are toast.
Check all the pulleys for debris wedged into them or nicks / bends
last thing is the tension spring.
If it is too weak it will allow belt to flap
naturally all the moving parts need to be lubed.
Check the pivot hole on the tension arm if there is one as they flog out oval.