To consume 320psi at this rate, the ascent would have to take only 2 minutes and 40 seconds, that's over the recommended 30 feet/min., and that's not even counting the need to slow down to 10 feet/min. near the surface. For all we know, the OP ascended too fast, not too slow.
Actually, we do know this, because he told us that his computer gave him an ascent rate violation (according to the dive shop).