There was some problem- hence the reply has come twice.
Apart from trains, volvo sleeper buses are available from Inter STate Bus Terminal at Kashmere Gate. These are night buses and take approx. 6-7 hrs depending on traffic. - Delhi -Dehradun is approx.260kms. Check out with
GMVN website for accom.(if not have already) Reliable, no cheating.
DDN Mussoorie is approx.38 kms uphill...
more... and plenty of buses are available from DDN. Enjoy your journey.
PS: I have already given a reply in the same number but unfortunately, it did not appear. hence i am replying again. The old one if it appears stands good. thanks and have a nice vacation.