I've failed multiple regimen and I've been off ART for a couple of months now. Do I need to go back on ART for resistance testing to be accurate (GART)?

If you have only been off of antiretroviral therapy for a couple of months, then it is likely that drug resistance testing will detect many (though perhaps not all) of the drug resistance mutations that your virus has picked up. The good news is that a drug resistance test paired with a good clinical history (what drugs have you taken, for how long, and with what associated toxicities and suboptimal responses were observed) are sufficient to come up with a very good new regimen in the vast majority of individuals. The sooner you get the test, the more likely you are to identify persistant drug resistant mutations.