White smoke is a cold startup issue. That is, if you can differentiate between blue smoke (oil) and white diesel stinky smoke. it's not so unusual and will go away in the first few seconds. If that is what is happening, it's a injector that is leaking. First few seconds of startup, the teaspoon of fuel that leaked into the combustion bowl will blow out in a white cloud.
The second issue, stumbling at 3,000rpm, is more likely an overfueling issue, either bad injector or the injection quantity on the pump is set for too much fuel. Probably both.
When you say you had your injectors 'pressure tested', my first question is 'how many miles on them? Original? Manual or Automatic? Who tested them? Did they check the 'leak down'?
I agree, it takes a fairly good test bench (maybe not $100k) to determine if a pump is good or not, but truthfully, the engine running with a VCDS is your first and cheapest 'test bench'. Many faults on a pump can be determined with VCDS and without a diesel shop involved.
Since it is unlikely you have VAG-COM, you will need some help. Check out the 101 section for VAG-COM locator. OR spend some money with a shop that knows how to use the VCDS or equivalent.
The first test is to determine what your pump and injector are actually doing. For example, timing, Injection Quantity, Idle Balance, fuel economy, how stable is the timing on the graph... those are things you are not going to get without equipment to look at your ECU. Otherwise, you are shooting in the dark.
Not sure I've seen white smoke due to a filter issue. What's the issueis if it's the EGR delete?