I had the exact same problem with my GT3037 and Walboro. You do not need a surge tank. That piece of shit Walboro 342 "255lph" pump, are crap. Once they go beyond 60psi, their flow goes to shit.
Do some maths - 18psi of boost (FPR is 1:1) + 42psi rail pressure + a few psi in pressure drop = 65psi+ of pump pressure needed. If your boost goes a bit higher, or other reasons, the pump needs to make even more pressure.
Once your flow drops off, the car is starving of fuel and leaning out. If you don't do anything about this soon, your engine will blow.
My advice, and I did this - Buy a Nismo 275lph pump, install, and all problems will go away. They are a complete drop in unit, come with the bracket, sock, cables, etc, and it takes about 5 minutes to put them in. Don't buy the bosch 040, their pickup is absolute shit.
If you do want to go cheap, buy a bosch 044 and do a direct replacement of your walboro.
You will most likely need a re-tune too, because if your existing tune was opened right up to accomodate for a failing \ inadequate pump, a new pump will make it as rich as hell. Your tuner should have seen this, instead it looks as if they have gotten lazy, or left it like this so you'll come back to be charged more.
Attached is a picture of the Walboro dying in the ass.