i just moved from colorado springs colorado (5k feet) to downtown LA (about 500 feet) After teh trip here, my car will misfire if i put my foot into it, and the rpms are above 4500. When it misses it feels like the knock sensor retarding timing. this is on an lt1 by the way. any thoughts?? im not sure if it takes a wile for the maf sensor\ computer to get used to the new air density. IS that possible, or what im thinking might be more of the casue would be that in colorado it ran fine on reg unlead, but here with the higher compression maybe thats not enough? any help would be awsome.

 

Higher altitudes don't need as much octane for higher compression engines. Try running a tankful of premium to see if the misfire goes away. Retard your timing back a couple of degrees also.

 

So after trying to run a few tanks of high test nothing has changed at any rpm's above 4000, she starts cutting out and missing.