My girlfriend had the same problem. I did a full tune-up.  PCV valve and all.  That didn't help.  It's good to do but didn't solve the problem.  I then had the tranny flushed.  WOW!!  What a difference.  The fluid that was in there was no good and was causing the valves in the tranny to stick = no power.  I would highly recommend this.  When I checked the fluid before it didn't seem to bad but it was.  I was all ready to change the gearing in it.  Luckily I tried this first.       It also helped out the mileage.  Don't expect to much out of an automatic.  Weakest part Toyota ever put out.