Curious questions

[rraccerr]

2014 t680 with a ISX 15 400 Cummins. Two questions i would need help with.

1. My sweet spot on my rpm meter is at 1300 rpm. That’s where I keep my engine running over the road. But I read that an ISX should be kept at 1650-1800 to get best performance, is this true? And if so, should I forget about that sweet spot indicator?
2. I would like to be as effective as I can to fix my own truck and I’m searching for the best way to purchase the insight and inline products. The best way to get everything I need to start my own diagnose and repair. A lot of online stores offer diffrent prices and deals. I’m confused as to what to purchase that will accomplish the the road I choose to travel.
Any and all help will be much appreciated. Thank you. :blush: