Just an update. Mostly onboard with this topic, though for 4m40 injectors...

I have been having fuel consumption issues, lacking power and a little more smoke than I did at first. I tried most of the common fixes, but little difference. This culminated in a camping trip where I pulled my little trailer, and the truck really struggled. Add to this my oil level bizarrely increased... so... I pulled the injectors the other day and had them tested at the shop Maurie referenced above. All the nozzles are burnt, and two injectors are stuck open and dumping fuel. Unfortunately I'm leaving for holidays in a few days, and so they're ordering the parts, and I'll yank them again when I get back, and have them rebuilt. I'll report back on the results. I'm imagining a dramatic difference.

Just fyi, my truck now has just shy of 100k kms. If your mpg is going down, or you're lacking power, this may be something to check.