There is no DehraDun Rajdhani Express, unfortunately. But I agree with you about the general experience about the trains running to DDun as we call it. By itself, DDun station is something of an enigma--caught between being a small city station and a big city one. The trains going there are either very long distance--coming from Guwahati, Gorakhpur, Kolkata, Mumbai, or then from Delhi which is a short distance. But try and get space-- no reservation is avilable on any train from the booking counter in AC class. It is always wait-listed. As usual, when you reach the train station and ask on the train, you get place. The trains to DDun are always crowded and the railways have the excuse that since they are coming from far away, they cannot be cleaned en-route. And the trains from Delhi--well, please go to Delhi or New delhi to board a train--any train-- and you’ll know.