Turbo 350 problem

[AusMarty]

I have a turbo 350 trans which is now out of the truck, it was rebuilt from previous owner, the problem is when you put it into drive it would hesitate before it would engage in forward and reverse, Oil level was fine, I pulled it apart today and found everthing is in really good condition, the pump clutches seals all look fine which is a bit of a worry because I don't want to put it back in and have the same problem, could it be the torque converter doing this ? it looks like it has been replaced also, it has a number on it 47011 which I looked up, summit advertise it as Boss Hog night stalker, the truck has done 3500mls since rebuild, any Ideas ?