Car stutters/hesitates like it’s two stepping when WOT

Just got the car back from having the top end fully re build and a brand new turbo. The thing is when I got it back and after I drove it a couple hundred miles I went to do a pull and it’s making a lot of air like if the turbo is just blowing it out and the car isn’t making the full boost like before it just to fill up the psi gauge that comes with the car that tops out at +15 now it barely hits that. After a couple of days car has gotten worse now it only goes up to the +7 mark on the gauge and air sound just got louder and a lot of popping and backfires small ones but there were not there before I’ve changed the spark plugs cleaned the MAF sensor and nothing seem to do anything.

 

First, dont do things that cause "popping and backfires"
Next, based on your info, look into a boost leak test. If you arent hitting targets, and hear pressurized air releasing you have a considerable boost leak. Dont forget to also check the tightness of the turbo to manifold bolts.