My Ford 6.2 gas does not need to scream, to pull my FW up a 7-10 percent grade. I've never needed more than 4K rpm, even double towing, up a 7% 3.5 mile climb, which includes lots of curves, and speeds of 35-55 mph. At 3-4K rpm, it is very smooth and quiet IMO anyway.
Maybe I'm more used to real screaming rpm, from years of riding crotch rockets? My current Yamaha FZ1 redlines at 11,500 rpm, and while it does have an exciting scream, it is very smooth running. First gear at redline about 90 mph. It has 5 more gears to go! Due to factory exhaust valve tuning, it will handle 40 mph in 6th gear nicely. Top speed 170+
The Ford 7.3 makes good HP and TQ, at lower rpm than the 6.2, and many other gas engines as well.
Jerry