So, here's the latest for those of you that may be interested. I spent this weekend in McDowell Mountain Park with the wife and our dog and found that that furance performed like it should at an elevation of around 1,500 ft. It dropped down to around 40and usually fired up on the first to second attempt. Today we drove up to Prescott (elevation 5,000 ft)and it fired up there on the third attemt on the first cycle. Just got back to Flagstaff (elevation 7,000 ft) and nothing! Can't get it to fire. So, after spending several days researching and replacing parts, the conclusion I've come to is that the Suburban NT-12 doesn't operate properly above 7,000 feet. If anyone out there knows of a solution to get this thing to fire at this elevation short of placing your hand over the intake port outside the vehicle during its ignition stage, I would love to hear it.