2006 Volvo Ved 12

Hello there, Have a problem with my truck
When I'm driving on the highway and the truck is running just fine all of a sudden
loses power and i can floor the gas but it can barely get to 50 m/ph from 9to 10 gear it needs a 5 minutes and after a little bit all of a sudden it just springs into action and runs back normally..doing 70 without flooring it.
The mechanics I left my truck with can't find it but keep replacing different things so far they change the injector 4, because this what they saw on the truck computer. but nothing I took the truck for road test today, it did the same thing. So what they are saying is they'll be looking for something else and at the end they my gonna have to replace the all 6 injectors.
So anyone ever experience anything like this before?

 

not sure if they have. truck still at the shop