It could be a number of things. Bad engine, bad tune, something not connected.
Just because it seems slow doesnt really make it slow either. My car with a 20G pushing 20PSI seems slow to me at days, but thats cause I get use to the power. Check ever last connection, ever line, be it power, or vacuum lines. Start simple and work up to the bigger things.
Is it on a break-in map? To break in the new engine? Who did the engine swap and if it was a tune shop. Maybe they throttled back boost to make sure you don't beat on the new engine. Which wouldn't be a bad idea because your pistons will probably leave little shavings in the oil until you run it and flush the oil once or twice.
378awhp/373wtq Custom Dom 3 & CBRD tuned 2006 STI.
"When in doubt...flat out" - Colin McRae
U had the engine swap done at a mom n pop shop I'm sure it just needs a tune I checked the lines there all fine although I did notice blow back buildup Arron's the alternator but the power steering pump is bad so I assume that's the cause not really sure tho