I run through the backbar weaving and then swap to the frontbar, I do the rotation and weaving but as soon as I swap to the backbar I loose 5-6k dps. Do I need to use a DOT before I swap?
If your DoT's are on the back-bar, then you will have a DPS dip while re-applying them, as most don't have an up-front damage component. And they're then adding to the DPS seen on the front-bar. So that pattern is expected, and averaging the DPS over a longer time, with multiple full rotations, is one of the reasons parses are done on the higher-rated dummies. The other main one being to factor in sustain.