When I try to engage reverse or drive, from the park position, it's a crap shoot. Sometimes it will, sometimes it won't. I have changed the Brake light switch. Yes the brake lights are coming on, but still won't engage consistantly. I find pumping the brakes helps, sometimes, to get it out of park.

 

Could be your brake INTERLOCK Solenoid is failing. The brake light switch feeds power to it when the brakes are applied. The Interlock Solenoid is located towards the bottom of the steering column.