I'm curious, when the belt is removed is there any damage to it?
The belt and pulleys works as a single system so changing individual pulleys and the tensioner will not solve the problem if even one of the pulley is out of alignment...
I work for a Diesel engine manufacturer so these problems you guys are having is kinda puzzling to me...
Normally for us, change tensioner, check pulley alignment, change belt... There will be belt and/or pulley damage if alignment is out...