Transmission not transmitting

While sitting in traffic there were a series of four 'bumps'. It actually felt like the van was hit. Then I noticed that the engine was whining. Being in the turn lane of a major road, I was committed. There was a slight hesitation in acceleration. Further up the road the transmission disengaged and re-engaged several times. Parked for a while and tried again. Same results. On startup the trans will engage for @50 - 75n ft. There after it will randomly catch then let go. One theory given is that the pump filter is clogged, not allowing fluid to the tork converter. Drop the pan, change the filter $150 - 300. The other is replace the whole thing ($2500+labor).