I don't think you're supposed to run the STX map on a stock WRX. It looks as if it has the same requirements as stg 2, which is a TBE (see the Cobb map list).
I did see the recommendation for running the STX map, but it sounds like it was only for the stg 2 folks to try. I personally haven't had any stalling issues in the 2 months i've been running stg 1.
Don't malign the AP without good reason.....sounds like there was some operator error involved in your problems.