Hey, I, new to the forum I recently bought a 2010 WRX. It has 33xxx miles with no apparent mods. I bought it from a subie dealer in my area that took it in on trade. It ran beautifully for the first 2 weeks, then I had the same exact issue everyone here is describing. It threw 2 codes the dealer attributed to a loose connection. They cleaned the maf and replaced the plugs and said I was fine. As it threw a misfire code ~1000 feet from the dealer when they said they "fixed" it they kept it for 2 days. The final diagnosis was bad gas, a vapor test gave a result of 6psi of the gas. I've cleared the bad gas, ran a few bottles of fuel system cleaner through and having the same issue. Up to about 9 psi of boost its fine, after that the car shudders and dumps boost. If I keep accelerating it will throw a misfire code in cylinder 1.
Sorry for the long post, but I really want to get this fixed, the car was amazing when I first bought it but now I'm thoroughly disappointed with it. Any help would be much appreciated!