I have a forester xt 04 with tbe, walbro fuel pump, catless up-pipe and td05 18g and has been tuned. When i got car back from tuners it was awesome. Boost was coming on nice in all gears around 3k and by 3.5k it was at full boost (17psi) all the way to redline. Even under light throttle she would be taking off at 3k and boosting nicely. Then after 3 or 4 days i was holding back in traffic in 2nd gear and put my foot down and i didn't feel my boost coming on. Looked at the revs and they where up around 5k. When i took off from a set of lights on wot it boosted fine. I installed a guage to see what was happening. When i'm in 1st, 2nd or third the boost guage doesn't get out of vacuum it rises and falls unless i'm on wot. I can redline without getting any boost at all under moderate throttle. However when i'm cruising in 5th the boost pressure builds and i take my foot off the accelerator the guage will drop to 20 vacuum and if i touch the gas again the guage will jump up to the pressure it was before i took my foot of the gas. So its not building boost pressure in lower gears unless on wot but builds boost ok in higher gears while light on the throttle. I checked all hoses, exhaust, restrictor pill, bpv, fuel filter. Took it back to the tuners and data logged and they couldn't find out what's causing this either. Has this happened to anyone else or does anyone know what might be causing this to happen. Any help would be greatly appreciated.