Have they pulled the covers . If not they need to .
A loose injector solenoid will show up on a buzz test .Without pulling the covers. Poppets cannot be verified without the visual , while they are still in the truck

 

Aha! They have not done that no. The mechanics around where I live suck ***. Serious ***. I'll have them check. Thanks for the tip!

 

Does it run OK when warmed up and on the highway? If it were mine I don't think I'd be spending my hard earned money on injectors just to solve a cold idle issue. I'd also check the glow plugs first and as has already been suggested, make sure the injectors are actually the problem. Doesn't seem likely at all with such a low mileage engine.

These 20 year old trucks are fairly complicated compared to say a small block V8 gas engine. You can't just take them into a shop that doesn't specialize in them and expect them to be able to figure problems out. And good shops that specialize in them are hard to find. And, if you take your truck to a shop for every problem it has you are going to need a lot of money.

My experience is that I've had to consider my truck as sort of a hobby and learn how to troubleshoot and do my own work. If I had to pay a shop I might as well buy a new truck.

Bob