rb25det neo in c33 laurel.

[stemo]

have recently put a reb25det neo stagea motor into my laurel have had it running standard 5 psi boost, it pulls hard in first till about 4000 rpm then it cuts all power for about 1 second then grabs boost again, sort of gives a whiplash effect this only happens sometimes and only in 1st and second gear,rest of gears pull hard all throughout rev range, engine is standard. any help will be appreciated to resolve this problem, thankyou