We took a trip from Omaha to Las Vegas a few days ago and averaged almost 22 mpg going 75-80. The swap is a 5.3 from an 05 Silverado. That includes running AC full time and mountain passes. The last part of the trip from Salina, Ut to Vegas was right above 19, which my average speed was around 85-87 and some very steep inclines coming out of Salina. I thought this was pretty excellent. I’m running 20” Camaro wheels with low rear end gears and a good tune. New O2 sensors as well.