99 R50 Pathfinder Auto Transmission shuddering and stalling problems

[KLL]

Dear friends,i need your help.first of all i was facing a shudder/vibration problem when car is locking up to overdrive(shifting to 4th gear) arounf 45 mph. for few times, i found that; when outside is cold, it tend not to release the gears even car was stopping, and it acts like it was manual and driver forgot to press cluth. RPM drops to 350 rpm or so and it shakes like mad and stalls. When it is hot, no stalls, no sticking .But there was lock up vibration/shudder anytime it shifts to o/d.

I took the car to AT shot to repair these issues, they actually overhauled the transmission , ripped aparts, replaced all bands, seals, filter etc. we checked shift selenoid valves with a multimeter as it is suggested on factory service manual for pathfinder.

I took car from them and shifting was smoother and ride quality was improved like new. Unfortunatelly i faced that low rpm stalls two times in past two months after overhauling.

Today nightmare returned back, i was driving on high way and increasing speed, road was empty and no slope to climb. while shifting to overdrive(4th) it shaked and shuddered as it did like before i serviced it.!!! i kicked down to shift it to 3rd, then relased pedal to make it able to shift in to overdrive it repeated same thing!!!!????

this is total frustration for me. in past i fixed lots of things on my cars, i can understand inner workings of machines etc. also I paid them ~1000 usd and they did their job and it was working fine for 3000 miles. what is wrong now?? what can be the real cause of this issue? it seems overhauling cant cure such problem and i feel that major reason is totally different than worn out bands or stell balls inside a/t case.

stall problem seemed somehow related to torque convertor or control elements, because, when it is acting randomly, i feel car is accelerating faster than normal,like a manual cluthc truck, but shifting is real hard, when i brake to stop slowly, it shakes violently and stalls. when engine is warmed up it dissapears in few minutes. next morning it is not there most of the times. other one is classical o/d shudder which i explained few lines ago.

any experience? could you please help to diagnose?