Update
I finally found some time to pull the turbo and exhaust off the truck again, as the exhaust leak issues were still out of hand. I tried the stovepipe cement but it worked no better than the pipe sealant. So I gave in and ordered a new uppipe from ATS. I tested it on the spare y-pipe and the fit was really tight, so I swapped it in for the old one and put it all back together sans the worthless and messy sealant. The thing's making up to 5 psi if I push it up to around 2100 rpms between shifts, whereas before it was making maybe 3 psi between shifts and 5 was the most I ever saw on the highway. I don't know what happened to that old uppipe but its not right.
So, its better, but I still think it should be making more boost. Fuel is turned up enough, wastegate is maxed, and turbo looks to be in good shape. So, I am gonna swap my other y-pipe in, since it is a tighter fit- so tight that I am scrared to try to put it on cuz it will never come off. IF that don't improve it, I will then give up and not worry about it. I am moving to Oregon in a month and won't have anywhere to wrench on the truck for a while.
That's my little update.