If your vacuum gauge is showing greater than 15" of Hg or more you have no vacuum leak. Most Coyote engines with stock cams run 17-19" Hg at an Idle of 750 after warmup. This is assuming that VCT is tuned correctly. If VCT strategy is creating overlap effect vacuum will be closer to static. For those reading who don't undcerstand VCT basics or cam basics...disregard.
Some vaccum leaks aren't apparent until throttle and load are involved.