I just got back from a week in Yellowstone on my Z and I think I have found a quirk in the EFI program I have not seen discussed here. At home (2200' ASL) my sled runs pretty well. I have been using solid pins instead of the stock hollow ones (still waiting for a clutch kit) and running the TRA in 3. This usually gives me about 7700 rpm and pretty good performance. My best is 116 on the speedo in far from ideal conditions. In Yellowstone (6600' ASL) I put the stock hollow pins back in and ran the TRA in 4. This seemed OK till I went up in altitude just a bit, like maybe 1000'. Then everything went to s**t. The sled developed a dead spot at 6500 rpm and would sit there for maybe 3-4 seconds before jumping up to 7500-7600 and taking off like it had a turbo on it. The higher I went the longer it would lay at 6500 before reaching full revs. Eventually, if you got to say 8000' it would never break thru the dead spot and would just sit at 6500 rpm. I tried the TRA in 5 but it made almost no difference. A trip to the local DOO dealer got me some Summit clutching (ramps and spring for 6000') and I thought it was cured as the sled was more responsive, but as soon as I started to climb the bog would return.BTW we have been riding at altitude for years and are very familiar with what it takes to clutch a sled for mountain riding, but this sled runs different. I am convinced there is a fault in the program causing this mid range flat spot. My local dealer at home tells me that the Summit opens the power valves sooner and this will likely fix the problem. I guess that means that every time you want to head for the hills you will need a trip to the dealer to have the computer flashed *%@!!!!!!!! The purpose of EFI is to meet emissions and NOT have to be making adjustments every time you ride a different altitude.Next I will have to find out I am going to be paying to keep having these programs swapped back and forth.