You may have got hold of another bad pump. Normally on BD machines, there is a short blast of water out the drain hose as the machine shifts into agitate and closes the port on the pump. But before you condemn the pump, check these items again.
I agree with Westytoploader's post in another thread about lubrication of the cam bars, especially since it hasn't been used in a while.
I would also look at the pump and the agitate solenoid/cam bar and make sure they are not binding up because of some foreign matter, lack of lubricant, a bent pin or a bent cam bar. Also check the cam bar spring (the spring that holds both cam bars to the transmission) and make sure it is tight.
There was one other thing that came to my mind, but, upon realizing you have a portable, would not apply. Sometimes, on full-size BD machines that have self-cleaning non-basket mounted filters, the side check valve gets stuck, causing some really interesting situations.