I agree with post above - we need more information. Did your dyno operator give you a print-out of the dyno? Many of them have the air-fuel ratio (AFR) as a scale and horizontal line on the bottom of the chart. If you have it and can scan and post it, that would be helpful.
How "lean" were you told it was? Opinions here will vary, but my view is that anything leaner (bigger number) than high 11's to low 12's under load is too lean for me.
Regarding your BOV - yes, it needs to be running in full recirc. Farting air to atmosphere for giggles is not good. With a MAF sensor measuring air mass on the unpressurized side of the intake your ECU then matches fuel it thinks is needed and shoots it into your cylinders at high pressure. When you fart some of that air back to atmosphere instead of sending it back into the intake track, there is a mismatch of air and fuel. It usually shows up in drivability problems, but eventually could result in the ECU "detuning" the engine to try to compensate. That's why there are credible reports of VTA MS3's dynoing lower than recirc BPV engines with otherwise similar mods.
However, VTA on our engines typically makes the engine run even richer, not leaner, so I have some doubts that is the problem unless you have a vacuum line to the BOV or some other vacuum line loose, pinched, cracked or damaged when you were making your mods.
Are you throwing any check engine light codes - is the check engine light on? If so, can you get us the code number (take it to Autozone, etc. and geta free code read) and give us the number. There are many reasons for running lean and this would be a big help.
Without a monitor(a borrowed Dash Hawk or similar device) of some kind to know what your AFR's actually are under different conditions, we're pretty much looking for a needle in a haystack right now.
More info please.
