randy toad

I hope someone can help i have a 99 uk car and the turbo does not seem to pull as much, its ok when you first start it up but after a while you just dont get the pull i have notice this especialy in second gear. its just had an engine rebuild as the head gasket blew and had new seals on turbo and various other bits and peices. i got the car back 2 weeks ago and its been fine until now with this problem has anyone got any ideas thanks