I'm using 60/ 40 PG/ VG on SmokTech Mega DC 1.5 and I get about 1 1/2 weeks- the Rez's are SmokTechs. How are you filling them and how much are you putting in?
I do my first fill with a syringe down the side in various spots. Usually just under 1.5ml for the first fill. Then I add a few drops down the side straight from the bottle every 3 hours or so. If I can see juice standing in it after 5 minutes I blow it out and use my syringe to suck anything that has leaked into the center. I really hate the idea do trying to clean these things, but we're talking 2 every 3 days at 1.25 each. Ouch!
Try placing a round toothpick in the center air passage and filling slowly until the filler is "slushie". I think some of your juice is getting into the air passage and causing problems. You may be also damaging the air passage with the syringe also. It's very fragile and once damaged it's game over IMHO.
I suspected that a little. They seem to make a sudden change from great to crap directly after a top off.