hey brownhillboy,
I've tanned many deer skins. First off, brain or egg tanning deer skins with the hair on can be done, but it increases the amount of work you have to do at least 4-fold. The grain (epidermis) of the skin is usually removed in the tanning process. If you don't remove it, it tends to form a stiff crust that will lock up, prevent the underlying fibers from stretching and resulting in stiff, rawhide-like skin. I've never tried tanning a deerskin with the hair on, what I'm relaying is just what I've read.
And yes, you need to pull, stretch, and work that skin until it's totally dry. I've softened deerskins that have taken 8 hours till they were dry. I softened an elk skin that took 9 hours. It's the most physical and testing part of the entire tanning process, but that is what makes them buttery soft.
I use the wet-scrape method that I read in Deerskins into Buckskins by MAtt Richards. It's a great book and results in excellent quality buckskin. If your skin isn't soft to your satisfaction you can re-brain (or re-egg it), and then stretched till dry, but usually it must be done several times.