I went with Saddle Skedaddle to Sikkim in NE India – Himalayan foothills – in this context a hill is anything up to 3000m!
The tour was fantastically well organised and it would have been extremely time consuming, if not impossible to organise without Skeddaddle.
They do tours all around the world inc Peru, Chile and Ladakh in NW India. The Ladakh trip gets up to 5000m from memory, the highest road in the world.
They do both MTB and road tours.
I cannot reccomend highly enough, the tour was some very physically challenging cycling and genuine immersion in local culture, food, religion etc
The local guides were from Rimo Expitions, an Indian company who mainly do trekking and mountaineering in himalays, but also cycling. They were very good, knowledgable and happy to give local view on culture and particularly buddhism. I have a feeling they operate in Nepal as well as India.