[chittychittybangbang]

I don't know why you replaced the lifters but it should'nt increase power. Extra air won't reduce power at all. Diesel power = fuel. If you have a performance chip the MAP readings will appear all messed up but since you didn't mention this I assume no. In addition, if you press on the throttle quickly it's normal for the MAF specified vs. actual to be off somewhat.

The most obvious is boost leak or clogged fuel filter. I know you checked for a boost leak but make sure you do a through check because often a small crack is not found unless you can pressurize the system.

Possible problems: sticking EGR valve, sticking turbo, Bad tank of diesel? Cheap nozzle causing a problem?

 

[chittychittybangbang]

What I mean when I say boost leak, is that before it was OK and now it's leaking. If you checked than rule that out.

A little smoke is at full power is normal and normally means more fuel/power so this suggests a reduction of fuel. The question is why? New fuel filter rules out that problem.

Since you have a scanner, log the EGR and boost function to make sure there's nothing wrong there. Also log the injection quantity while normal driving and full power. Here are some tips and background info on injection quantity: http://www.myturbodiesel.com/1000q_how_to/multi/IQadjusthammermod.htm

 

[chittychittybangbang]

Did something clog the snowscreen before the air filter?

 

[chittychittybangbang]

correct, check the IQ again.