Do you have your tire pressure dialed in? Coming from a roadie background, it can be psychologically difficult to go as low as you really can. Make sure the tires are right for the type of terrain you're riding, too.



Mastering Mountain Bike Skills by Brian Lopes & Lee McCormack seems to be the standard recommendation if you're looking for a book. I have it, and it's good. I don't think there's a lot of climbing advice in it though--can't remember for sure, it's been quite a while since I've read it.


https://www.amazon.com/Mastering-Mountain-Bike-Skills-2nd/dp/0736083715/ref=la_B00K1RWS9I_1_1/140-9980682-0628856?s=books&ie=UTF8&qid=1492523781&sr=1-1