Which is correct / acceptable usage
I pride myself associated with CompanyX from past 3 years.
I pride myself associated with CompanyX for past 3 years.
OR something else?
I pride myself for being associated with CompanyX for the past 3 years.
for indicates a period of time.
If you were to use from (which indicates a starting time), then:
I pride myself for being associated with CompanyX from 2013 to 2015.