If your climing revs and holding boost all the way through without dropping off I don't think it's a boost leak it might be worth adjusting your TPS on the inlet mani, it may not be opening on time fully, the compressed air maybe getting pushed back onto the turbo then fully opening it's just a hunch though read your boost gauge at high revs look for any boost drop off you don't need to use a dumpvalve but it does take pressure off the turbo. What boost are you running (spring)