Difference between Injector Pressure Regulator and Fuel Pressure Regulator

Hey guys,

I have an F250 6.0L Power Stroke Diesel. It started shuttering between 50-60mph with steady fuel. I found out it was probably a bad fuel injector on this forum, so I joined. I took the truck to the shop and they replaced the (from the work order):

4C3Z*9E527*BRM REMAN NOZZLE ASY
3C3Z*9T517*AG Kit - Pressure Regulator
Both Fuel Filters
3C3Z*9N184*CB ELEMENT

The test code was P0278 #6 injector misfire.

The next day when I started my car. A new puff of whitish smoke came out of my tail pipe, but only after it had sat over night. I came to the conclusion that this was probably oil or coolant. I sort of ruled out coolant after looking into it and oil was what I decided it was. (again using mostly this forum). I took it back to the shop, now they want to replace the:

4C3Z9B246F: Injector Pressure Regulator
CM5126: High Pressure Pump Coupler

So my question is any idea what happened? I now get white/grey smoke when it's been sitting for a while and it takes a long time to start. Could the first repair have caused the need for the current one (that started the day I got it back). And is the IPR the same thing as the FPR?

Thanks in advance,
-Ryan