Re: Leader length
I agree with Kytroutbum on the length of both leader and tippet for the park for general fishing. *Nymphing, you can add a little more tippet if needed to get the fly down to where the fish may be depending on how and where the fish are feeding. *
If you are having trouble getting the leader to turn over, you might could try a lighter weight leader. *I don't know what size you are using. *Brand may play a role also, although I've never experimented much with different brands. *Orvis Mirage and Frog Hair are all I've used and they perform well.
Proper presentation on short casts can be difficult sometimes because you're not generating much momentum with the line to really engage the rod. *Try going into LRO and casting different rods short distances to see which one may work best for you. *Sometimes a different type of rod can relly make a lot of difference. *Any of the staff would be helpful and informative.
Good luck! *
May you fish more than you wish for.