Long canyon drive, loss of power, high elevations

[Jaybird09]

I have a awesome little scoot (Honda pcx 150) that I drive every where. And I mean I drive this thing all over the place. I live in utah and we have some big, long and high elevated drives. I went up a smaller canyons all summer and it has always handled great, last night I decided I would take it up a Ogden canyon and hit powder mountain. It was doing awesome till I got bout half way (45 miles) up the canyon (this is a steep and big mountain drive) and as the air got much much cooler and as I got higher up the canyon the power just seem to go away. I was cruising up the bottom of the canyon at a cozy 50-55 but the higher I got the slower the scoot went. At one time I was only pushing 32-33 mph and I had to pull over and let traffic go around. Frustrated and confused of never having this problem before I turned around and head back, I gained power as I came down witch made me start to think... Is the thinner, cooler air at high elevations causing my scoot to loose so much power to cruise at 50 all the way down to 30? I'd like to hear what y'all think would have caused this.... I have drove it all morning into the afternoon and she has all the power she has ever had and runs perfect.