I'm 6'1" and ride 23"/58cm road bikes. I have an old 19" '94 Gary Fisher hardtail that I wonder if I'm too big for, but I'm not really clear on mountain bike sizing variances. I will say I am having a harder time getting through technical terrain (especially climbing) then I remember from my last foray into mountain biking. Of course, both me and the trails are probably in worse shape (I bike 8-10 miles a day, but on the street with a road bike - totally different)

So is it me or is it the bike?