Basically you get the stickers on the side of the bed, upgraded suspension package (shocks, springs, etc.) and a rear diff. locker. Worth the price. You should make sure the Taco you're looking at is indeed a TRD spec truck. Look to the left (I think) of the steering wheel and there should be a button that says "RR DIFF LOCK" or somthing like that. The '99 is "second" gen.

 

Thanks for the information.