With the load of the AC on the engine, 10hg vac is normal.

Why were you messing with the wg arm nuts? As long as they are adjusted so that the flapper stays closed with the tension of the wg spring it should be alright. But unless you are transfering a wg to a different turbo, you shouldn't have to ever mess with those nutz.

I did have to transfer the wastegate. I sold my other turbo but not the wastegate and the turbo I bought didn't come with one.

Was it driving/boosting ok after you put in the new turbo and then this happened? Either way, definitely get the turbo out to get a better look at the wg. You should be able to get it out in an hour now that you've already done it once :) You don't even need to remove the airbox!

I had what felt like a boost leak after the install. I drove it like that for a day or so until I could get it back in my garage, but on the way home, at a stop light....bam, no more boost.

Get that turbo out.

What am I looking for when I remove the turbo?

A wastegate arm/flapper that doesn't close by itself or have slack in it. The flap should be sealed closed. It should take some effort to manualy push the wg arm to open the flap on the inside against the force of the spring. Make sure the outside fins turn with the inside fins.

And if all of that stuff checks out, then it has to be a boost leak that I just need to keep looking for?

Your engine would flat out not run smoothly, if at all, if you had an external boost leak large enough to register 0 at the manifold. If the turbo was working, you'd hear it. If you had a leak and the turbo was trying to work, you'd REALLY hear it. If the wg is not closed when it should be, that is an iinternal boost leak, and if that were the case, the engine would run pretty ok considering you have the equivilant of a brick sitting in your exhaust.