Dude, I had almost the exact experience in the half marathon (which is like a marathon to my uninitiated self) - minus the walking and the sunburn. The morning heat and humidity were most unpleasant, though I was finished by the time you faced the worst of it. I trained my long runs easy - in zones 2 and 3 - and figured I could step it up to near LT on race day. I did, but I ran slower than my long training runs. How on earth does that happen? I'll join you at Pizza Hut next spring.