ML320 2000 AT die occasionally

My ML320 2000 automatic start dying while driving. RPM will drop and it just die.. start the engine, fire up and die instantly.try to start the engine for a dozen time still the same...I leave the car on the road side. Return in about 30mins. it start normaly and quickly drive home.distance is around 3Km. 2days later I drive it to a nearby Workshop. when almost reaching the workshop, it happened again.RPm drom and engine going dead. I stepped on the gas pedal deep down, it limped and stop and limped and stop. made it just outside the workshop. Good enough for the mechanic to test the engine when the problem is there. The mechanic test the fuel pump relay, check all the fuel filter and fuel pump socket. all are in place and clean. tested the fuel rail and all are normal. get the engine scanned and noting was wrong.after a 45min testing here and there, the engine suddely able to start and is normal. The mechanic tested the car drove it around for 30mins, nothing wrong. Car was running strong.Tested the car for a few days and the problem is gone.
So i was not charged a penny. i drove it home all is fine. But i still have doubts on the car and dare not drive around..the car has always been my wife daily ride sending my son to school..I doesnt wat them to be stranded on the traffic or roadside.... So I start the car everyday and try to see if problem came back. after 2 min, the engine just died..start the car, it started right up, stepped on the gas, all is normal..so I checked all the sockets and cable and open up the fuse box. nothing that I shake or move make the engine die. So I try hitting the side of the fuse box, the Engine shake and like it wanted to die but normal again. i try hitting the box again for a few times, it shutter again and rpm like dropping, then back to normal. after that I try hitting it again harder and harder but no more shutter and rpm drop. I rev up the engine again and again. all was normal..i leave the engine running for 1hr. all is perfect..
The question is could it be a loose wire under and inside the relay board. i would like to open it up but afraid that i would do something wrong. Below Re the parts that I have changed in 6-8mths time. Been owning this car for 7years and it is really reliable and comfortable car. My wife love iit a lot. but because of this, she start losing trust. i dont dare to drive the car around because the Culprit to the problem have not been identified specifically. Anyone have any idea? Really appreciate. Thank you.

Fuel pump Bosch ( replaced because of dead fuel pump )
Set of new Coils bosch ( 2 dead, change a set )
Fuel filter ( replaced in case the old one is dirty )
Crankshaft and Camshaft sensor bosch ( replaced because suspect the dying of engine caused by this sensor )