High altitude loading up

you need to drop the main jet down to a 150 or 147.5 see if it doesn't get better.

take off the air box cover and see how it does..if you go to a 147.5 and it does better with the lid off you may have to go to a 145,just be real careful if you go down in elevation
on our trip to colorado i had to drop from the stock 152.5 down to a 140 and still had to take the lid off the air box at anything over 11000 ft.we stayed at 9000 and it ran fine there with the lid on.next year i will drop down to a 137.5,that should do the trick.

Go down two main jet sizes and add a dial-a-jet...Ive used one for quite a while on mine and it works well.

I use it for drastic temp changes instead of altitude changes, but its the same principle....

Look here:

http://www.thunderproducts.com/dial_a_jet.htm