2003 volvo isx15 cm570 issues

[Pd6cas2]

I agree with Rawze , shift between 1650 or 1750 depending on load and Hill , sometimes just stay in gear longer.
I have a 2001 CM570 , you mentioned colder temps ..!Im from MN and know the cold does slow these engines down, I've run -38 to -45 and with proper care, No problems ..
Ive replaced every sensor on that engine, especially Cam& Crank they made a world of difference. I have 3.1 million and 2 overhauls..
Being Your truck 2003 ,.. Fuel lines would be my First replacement, then All sensors.
Pull valve cover off and inspect all rollers cam etc..
Overheard ..
Ive also replaced main engine harness and ECM ....
Your in the right place for help..
But Rawze doesn't have a bullshit button' he will call out shi#t ASAP..