Did you take the pump apart to see if it has been rebuilt?
We have had some re manufactured pumps in recent years that made no pressure when installed, we took them apart to find they were incomplete (missing bolts!!). My builder now rebuilds his own pumps. Trying to save $100 bit us in the a$$ twice.
Sorry to hear this is happening to you, rebuilding the 4r55e can be a real process some times.
Who rebuilt this unit?
Do you have pressure gauges?