Where did I go wrong with alignment

I have a 75 Mustang - this is the second time this season I have fiddled with the alignment - first try after printing out and following the alignment posts from this site I was not quite sure on a couple things and contacted FFM for some advice on my oder setup - second attempt on Friday evening went good and I was very confident I was under the .003" and everything felt real good... well I took the kids out first thing Saturday morning and I felt a small vibration right after putting the boat into gear that I had not felt before (really conscious of things on the boat due to its age) the vibration was only felt at idle speed - anything over about 800-900rpms and the boat felt real smooth

where did I go wrong? or am I just being too super conscious of trying to get things perfect and letting my mind take over

there doesn't feel like there is any slop in the bearing and I have never had the shaft off the boat to check straightness there is no evidence on prop or strut of every hitting anything that would affect the shaft - the alignment was not very far off when I initally checked it - I only had to raise the front of the motor about 1/4-1/2 turn to get it aligned - maybe I should pull everything apart again and recheck the alignment

open to suggestions