Strange pressure reading and symptom

[greasemanicure]

On our 96ES with a 4R tranny, something odd happened today. I've been driving with a pressure gauge for some time and today when I put the EX in reverse, the pressure went up to about 180 as it had been but after backing for some time the pressure nailed the gauge above 300PSI and the EX coasted to a stop. As I had taken my foot off the gas, the pressure came back down and after stopping, it did the usual creep in reverse at idle. Did the same again after a second trial.

Two questions: What would cause the pressure to jump like that? What would cause the tranny to act like it went into neutral? and Are the two related? I guess that is three but who's counting. Any help gratefully acknowledged.
Joe

 

[JK080]

I have had one do this for me but I didn't monitor line pressure but it would loose reverse like that.

I replaced the valve body to get ride of it, possible worn valve bores in the valve body.

 

[greasemanicure]

I replaced the VB about three months ago. Before that there was no reverse and much slip in forward gears. Also adjusted the bands at the same time. What shocked me was the way that the pressure snapped from 185 to off the gauge in the blink of an eye immediately when the EX coasted to a stop.