No need to change the MAF if you change the injectors, but it will need a retune

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Have you been monitoring the boost to see what you are making? I was told to get an OEM maf and that would make tuning much easier and better to dial it in. Don't descreen it also, like some have done.

 

If you are dropping to 25 psi under any kind of load you are way under pressure for even an NA car, much less a boosted car. I suggest you stop driving it b4 you damage the engine. First try a regulator cause i had issues with my stock one after awhile. While it would hold vacuum, it wasnt functioning properly. Slapped a different stock one on and it no longer dropped under boost. I knew it wasnt the pump cause I had just swapped in a walbro not long before this. Also, if a pump has been put in, you need to check if you still have the sump in there, and if you dont, DO NOT run the tank lower than 1/2 or you will get fuel slosh and pump will lose prime. Another valuable lesson i learned the hard way. If you dont have the trap door already cut under the mat, look into doing so, makes life alot easier and no one will ever see it anyways.