2014 Volvo losing power at certain speeds.

I had similar issue with freightliner ...it happened to be battery connectors loose

 

When you replaced the injectors and turbo did they check the egr cooler, egr valves? Are you getting any ecu faults?

 

Yes my first thought was its a process of elimination however looks like you've already done that with the filters did that include the air - cleaner filter, if that's clogged up it'd certainly restrict your power. Next thing if you've done all of that is the fuel injector's depending on how many miles/km you've done if the pistons and rings are wearing out you could also lose power however you'd also notice it chewing up quite a bit of oil if that was the case. New or re-conditioned turbo check to see if that's also working properly.