If I go up past this, the taste really starts to taste burnt. 3.8 makes it really bad after a few hits. And it just gets worse from there with my tests.
Just to let ya'll know, I have been using air controllers, and trying my best to put forth what I would consider a "milkshake draw" - nothing seems to make a true difference. Sometimes, the taste is somewhat tolerable, but even then, there's a metallic layer that, like any metallic hit, makes my gums hurt around where I have fillings, so I know it's there. But most of the time, the taste is quite bitter and most of my tests on this device simply make me pucker and go "Blegh". Sometimes it's more of that fish-oil weirdness.
I have one last head left, and I'll be testing Velvet Cloud Vapor's Caramel Swirl which was a free sample. I've already tried the juice in a CE5 and it wicked like a turtle, which points to a problematic liquid. This test will be to prove if thicker juices may somehow have a positive effect on the Aspire's suction and wicking, as another user is having great luck with Aspire + VCV. The juices are %100VG + Distilled Water. Will see!
You might consider washing the last head thoroughly before using it, if you haven't already. It sure sounds like you got a sample of heads coated with leftover machining materials