I was scanning my car tonight and when I go into WOT the voltage drops to 11 volts. Does this mean that my alternator is bad and that i need to replace it. During normal operation the voltage stays at 13.5 volts.

 

Most likely the brushes are worn, or the brush holder is burnt or both. Average output voltage wise should be 14-15 volts a little off idle. I have rebuilt many over the years and generally when you see diminishing output as rpm's go up it's a brush issue. Rarely does the rectifier pack or voltage regulator fail. www.alternatorparts.com sells overhaul parts, and if you are moderately handy and can use a soldering iron you can service these units for a fraction of the cost of replacement. Places like NAPA generally sell service parts as well.