We just returned from our 1200~mile Christmas trip with our 5.4L F250 towing our 8500~lb mid profile 5th wheel. We maintained 65mph easily in the hills of the Florida Panhandle on I-10. On a few, it downshifted to 3rd to run 4200rpm but never struggled. We had plenty of power. However, I decline to recommend the 5.4L or any other gas engine to anyone due to most people's fear of letting it run in it's normal operating rpm range. The only letdown this trip was 7.8mpg bucking a cold front headwind heading west versus 9.2 heading up I-75 with a slight tail breeze.