Tacoma Gear Shift Problem

My new 2004 Tacoma Double cab, has problems with the gear shift. If I park the truck facing downhill on a pretty good slope, the gear shift can be jarred and will move between park and reverse. This allows the truck to roll foward. My dealer is telling me that this is how the truck was designed and all Tacoma Double cab models, years 2001 through 2004 do this. Has anyone else experienced the problem? The truck has less than 1000 miles on it and I feel that this is dangerous.