Only you can know that. First thing to check is if the hi altitude compensation system is working. I have no idea but it is there and in the factory manual. I would try it a little lean than adv the timing a bit and see what happens. Might take a while to get right. I used to live @ 7.5K and worked @ 10K. I had to drive up to 13K to get over the ridge to the city. never really worried too much about it but the first time I got it down to sea level I was amamzed how fast it was.