$COST had a difficult time at its 2.27 Fib at $808 this week but it appears to be following the market very well too, so this pull back may hold before going slightly higher as shown but I don't believe there is significant upside from here.
The 2.618 Fib is the upper limit of a Wave 5 and it is here at $863, so this level can not be ruled out
For me, Wave 3 and Wave 5 are looking very extended now for a company which is very steady but has limited growth now and overvalued fundamentals at this point.