Look up your engine and transmission. Most have a chart someplace that shows peak torque at X rpm. That gives you a starting point, once you know that you can play around with various shifts in that range. Otherwise its all trial and error as even 6 trucks with the exact same setup will shift at 6 diffrent places.
Yep. Some engines rev higher. Some transmissions have thumb splitters. Some turbos have more lag. And bigger HP engines will grenade drivetrains much easier so you progressive shift them. Well, I do.
Listen to the engine. She’ll tell you her dirty, dark shifting secrets. *lights after shifting smoke*
If you're heavy, shift at a high enough RPM that the engine will still be above peak torque when you start the next gear.
Progressively increasing the rpm for each gear. Example: 1st to 2nd at 1000, 2nd to 3rd at 1100..... 9th to 10th at 1400.
1400 for your baseline in low range. You might adjust that 50 rpm either way. 1450 to 1500 in high range as a baseline.