Re: Hi altitude(Colorado) vs Lo altitude(Nebr)...performance
I've driven N/A and turbocharged engines throughout the US and Canada and never noticed much performance difference in high altitudes. Most was about 7200ft above sea level, so I'm not sure how high you're talking about here. If you go above 10K, I can see altitude becoming a problem as the oxygen gets rather thin.
I'd get the vehicle checked for codes, some might be stored that you may have missed if the engine light flashed. As you mentioned "it died half way up the hill" leads me to believe that you have more going on than a change in altitude.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!