Is cool to just upgrade nozzles or is it much better to change the whole injector?

 

Depends on how many miles you have and the year...if I had a pre-2006 with more than 150k on the stock sticks, I'd replace them with new bodies and custom tips (i.e. use the stockers for cores).

I ran into a problem where the injector "failed", replaced the tips with aftermarket, and then had issues with a solenoid...it was frustrating to say the least, and I fought it for over 10k miles. My injectors were in/out of my truck no less than four times, which sucks when the good diesel shop is over two hours away. In the end, it was new bodies and the tips that completely solved my issues.

 

Replace the whole thing and put a 2 micron filter in front of the CP3