Can the GRE Sub in Psychology compensate for my low GPA? I am a psychology student. My GPA is quite low: 3.6 for first 3 years but 2.8 for last 3 years ( I spent 6 years in undergrad because I transferred and lost 2 years of credits). However, I will have a publication in psychology and strong letters of recommendation from professors. The low GPA is my major weakness... I am wondering if a good score in GRE sub (like 95 percentile and above) would compensate for my GPA?

Thanks in advance!
Almost certainly not. Although I'm not in psychology, I'm in the social sciences and we generally do not consider the GRE subject exams to have much probative value in regards to the ability to do doctoral work in a field. 

Remember that the admission committee is not trying to evaluate whether or not you score well in standardized tests, but rather whether you are capable of rigorous coursework followed by independent research. Our best way of ascertaining that is from your letters of reference and your statement of purpose (and to a lesser extent, your undergraduate grades).