I have 1 tuned with a 65mm and 1 tuned to a 62mm... I get 24mpg for the most part. I am not at 5400 ft, more like 800-1000ft....so I don't know how altitude changes that. I have modified manifolds on both mine as well. Hope to do a rear end change sometime before summer...spring hopefully... I think your times are good compared to Isky's 1st runs ...