Pouring injector cleaner Into a fresh fuel filter..

I have 415,000 on original injectors. I have been using cleaner in the fuel from time to time.

Thoughts

That would be a question for the additive manufacturer, or perhaps it's on the label. Other helpful info can be found in the SDS. You need to know the maximum, safe concentration for your engine. Many older Diesels will digest just about anything. Late model high pressure systems are much more sensitive. Many/most additives contain or are based on petroleum products, and what isn't (compatible) petroleum, is something else. Petroleum products, in general, are a wide range of chemistry, many of them harmful to the engine in higher concentrations. The balance of the formula is likely something you wouldn't want a heavy dose of. High concentrations added to the tank are still very diluted, compared to a 100% concentration, like filling a filter.

My truck holds 34 gallons of fuel, seems 4 oz in that 34 gallons is really thin..

Perhaps. It depends on what's in the formula, and what's in the formula that's benign or not beneficial. If the label suggests that 4 oz. is enough to treat 34 gallons, then either a full-strength dose would certainly be harmful (or just not run the engine), or it's snake oil, with no actual helpful properties. Check out the SDS and know what's really in the stuff.

There are Youtube videos out there that show Duramax owners using a GM brand injector cleaner. You disconnect two hoses to the fuel supply/return fittings on the top driver's side rear of the engine and in their place clamp on two hoses, which are run into a gallon jug with the injector cleaner mixed with diesel fuel. Start and let it idle till gone... about 45 minutes. Like most videos, there's no injector disassembly to show what any improvement might look like inside before/after, though they did show balance rates before/after, which tended to show improvement.

Here are a few links... https://www.youtube.com/results?sear...jector+cleaner

Thxs MP, I’ll commit those videos to memory..