mine does this to, and i got about the same setup, subs, hids, heat all that stuff and i also have a battery with a dead cell, and a weak(factory) alt
when mine does it, the dash lights go real dim and the left headlight flash's(hid) like its bout to go out, but it only does it when the rpm drops under 900, even when the cars warmed up
im checking all the ground first then doing the 3 big upgrade in a couple weeks
so ive sub'd to see what other say