I just installed the boost gauge. I am sure there is no leak. It hits a max of 17-18 psi tapering to about 15 by redline. I am getting a custom tune on the SLC trip. I really don't want a mbc, so my question is will the flash raise the boost up to 20 psi like it should be, or what?

 

It'll raise boost but itll taper down. If you want to run steady boost up top, try a stronger wastegate actuator.

 

No, don't touch your WGA. Just get an MBC - it's not a big deal. If you don't want an $85 reliable MBC, then you'll just have to make due with the flash-based boost, which should be around 20-21psi.