SS SLP2

iTrader: (8)

using a wide band to check A/F, last time I checked ( been a little while ) was running 12.3 -12.8 after rebuild and installing a vac modulator and 4000 yank ( was running 3600 yank ) after going threw a brake in ,500 miles I find @ WOT running 13.2- 13.4 . I do not think I have any vac leaks . MY question- SHOULD installing the vac modulator cause my A/F to go lean?
Thanks for any/ all replies
Johnny