I am working on a Hyster at a customers and the problem is this unit has very low power when you first start driving. Now I believe this is not and engine problem because while in neutral using the hydraulics there is plenty of power I can full out tilt and steer hard one way and the engine powers right through it. And as soon as I try to drive if feels like I'm starting out in second or third gear. Could this be the torque converter??? Or maybe filter problem.
Once this truck gets up some speed it really works well. But if you have a load on it and try going up a little ramp if feels like it is in second gear. ( this truck has only one gear and is Automatic)

Any help would be appreciated