Bricksters:

Last month, my 90 240 wagon (140K) bucked and stalled out intermittently. The volvo mechanic replaced the main fuel pump and fuel pressure regulator.

It solved the problem until now.

Yesterday while driving on the freeday, the wagon hesitated and rocked as if going over bumps. I pulled over, shut off the engine, waited a minute, and restarted. The wagon was fine and the problem only resurfaced later.

This is really pissing me off now. I sunk quite a lot of money and problems doesn't go away. In addition to the main pump and FPR, this wagon has a new transfer pump, temp sensor, and throttle switch. The fuel filter is fairly new.
I will put in a new 25 amp fuse today.

Any suggestions will be really really appreciated:

My thoughts are

AMM
crank position sensor
ECU (my is a 561)

But can AMM or crank position sensor give intermittent symptoms like this?

Regarding ECU, lots of bricksters suggest replacing 561 with a 9XX model, but FCPGroton catalog says that 561 is for models with EGR and 9XX is for models without, are these interchangeble?