Is there an adjustment for the stop light switch on a 99 GMC Yukon. I have replace it and my brake lights still do not work. Park lights work fine.

There is no adjustment. The park lights are on a different circuit than the brake lights.
Do you have a third brake light that works. Its also on a different circuit but works from the same switch. Do your turn signals work. They use the same filament as the brake lights.
Also, the brake light circuit goes through the multi function (turn signal) switch.

Since the brake lights and turn signal lights use the same filament in the bulbs, the brake light circuit will pass through the turn signal switch. When a turn signal is used it cancels out the brake light for that side.

Let me know if your third brake light and turn signals work in the rear.
Also, if youy have not already, check/change the bulbs. The type of sockets those lights are in also get burned so look at them well.