There's probably a very basic answer to this that a good mechanic can tell me. Last night I was driving up a short but steep hill (San Francisco, can't really be avoided). The cat was really sluggish and stalled right as I got to the top. The brakes locked up, too. Thank gods it didn't happen ON the hill. I put her in park and with a couple of tries was able to restart her and the rest of the trip home was fine. Does anyone have any idea what could cause this?