Languages are vast oceans of meaning and composition -- 90 hours simply is not enough for Chinese (or any language, really, reality itself is too complex to describe with a system that simple).
I'd recommend learning the characters using Heisig's Remembering the Hanzi (this should take about 100-200 hours), and then shifting to HSK (which should be pretty easy post-character learning) + full sentences.
If you like Pimsleur, keep with it, although I get made fun of for sounding like a northerner a bit from using it for pronunciation help when I was beginning. :)