2010 Volvo vn cold weather problem

Hi there just wondering if you guys can help me with this 2010 Volvo vnl ..
I live in Canada and when the temperature drops below 15 Celsius my truck starts sputtering under heavy load, loses power, can't even keep it below 1500 rpm ..
Everything comes back to normal around-5 celcius.
Any ideas what's happening? I really appreciate some help..dealers only throw parts at and the problem is still there
Thanks

 

I did all that..truck radiator is covered and I believe I use a lot off diesel additive..changed the filters.
Also truck is surging on high idle but only at coolant temperature above 170 F
Any ideas?.

 

New Turbo, egr valve, new injectors fuel filter hausing, clean dpf filter ...all this in the last 6 months, and still not running right... I believe you guys have to be right..have to be something that Volvo dealership is missing!!??

 

Latest update on this issue..
Truck is fixed ..injectors and injectors cups replaced..all my problems are gone .
As a mention this was the 3rd time since last July and volvo dealership in saskatoon refused to replace them in warranty because ..Cote " not bad enough to be replaced now..truck was missing on high idle but that's not bad enough "
I took the truck to lethbridge

 

Volvo dealer in Lethbridge spent 2 hours on diagnostics and took the truck for a test drive..they find air on the return line and the engine missing under load..
When they removed the injectors they find 4 bad ..next day afternoon I was back on the road with the truck fixed..
Saskatoon Volvo kept the truck in the shop for 2 days... they performed 45 minutes of diagnostics and they come up with " could not reproduce the symptoms for bad injectors "
I will not recommend this shop to anyone..