Help! Player walking up ramp onto vehicle

I want my player to walk up onto the bed of a truck, up a ramp. It seems that no matter what shape or at what angle or height I make the collision mesh (no exterior mesh angles less than 90) my player stops at the edge of the mesh. Player can load the truck when he jumps over the mesh edge, but cannot _walk_ up/over it. Changing variable "maxStepHeight" in player.cc has no effect.

When I instantiate my vehicle DTS file as a TSStatic object, it works fine. (I placed the shape at various z heights to make sure the collision mesh was functioning as expected.)

So my question is, why does the collision mesh function differently between WheeledVehicle and TSStatic, and how can I get my player to WALK up onto the truck bed? Thanks.