Lean codes can definitely be the result of a vac leak (or fuel starvation, bad MAF, bad sensory input from other devices, etc). A lack of fuel pressure or MAF issue can REALLY rear their head at WOT.
IIRC, you are going to do some vac testing to watch for a drop after sustained constant RPM's (checking exhaust restriction). Since you will have the gauge hooked up: In general, look for about 20" hg of vac at idle.
Good luck.