Needing advice on keeping an engine good

So i work for my cousin who farms 800 acres of row crop and he bought a semi last year finally. I used to drive his gas trucks and they were turds, always had the rpms up in the sky and split shifting to save my soul. The truck is an 07 international 9200i with a c13 cat holding 717k miles. 10 spd tranny. From what ive read the motor is an acert engine, some forum said if it has twins its an acert. On other forums i have read that if you drive them without hod roddin them they will last but if you work em too hard they can break. So id like to know how i can drive it to make it last. Right now with the 10 spd there is about 400 rpms between each gear and in 9th i can take most hills. It runs about 1450rpms going 45 in 9th. We are in pretty hilly areas so i take alot of hills. Is it working the motor to hard if i let it torque down to 1150 or 1200 on hills as long as i can crest over or will it be better for the engine if i just take it down to 8th and let her run 14 to 1500? I really wish it had a 13 spd, id like to try one and i feel being ble to go down half a gear instead of a whole would be better on the engine. Thanks for any advice to a new driver

 

It is a 3.90 rear as memory serves and currently i let it run to 1200 before i downshift. I have yet to floor it, havent seen a need to, so my rpms always drop going up the hills. I cam hear the boost die out a bit and it wont build up anymore with more fuel so thats why i downshift. What exactly do you mean be patient with the pulls?

 

Where also might i find the serial? All the hills i do encounter are short and normally only require going to 8th unless i want to slow down for an intersection i know is coming up

 

This is gonna make me sound dumb but thought these cats got peak torque at 1250? So i shoulnd.t let it go below that? I shouldve put this somewhere in the original post but when the boss bought it he was told it was set to 470hp and that you should upshift at 1400 and downshift at 1100. Thats what we have both been going off of. It doesnt buck at 1100 when on the hills. Only pulling 73k average though. Doubt the boss would go for adding stuff. If it dont make money....

 

Ill try and locate the serials tomorrow when we arent harvesting

 

Pretty much yeah. This is the first diesel ive ever driven and have done researxmch on motors and shifting and such so that when he put out the money for a gokd truck i could keep it good for him. What exactly is the sweet spot rpms range wise?