My belt is slipping very badly with my 178 with about 19k on the belt. I'm pretty sure the cause was a little oil either leaked or was spilled on my belt and pulleys which pretty much nuked my belt. I will be cleaning my pullies off today and installing a new belt today along with pulley saver kit hopefully this gets rid of any belt slip on my 178 pulley.

Stick your hand down in there and feels some of the pulleys and see if they are covered in grim and oil like mine were.