Car stalls while driving, Idle is smooth?

I just picked it up from Nissan. 20 miles later it’s still running. They told me that the fuel pump relay was loose, and the exam ground wire was also loose. I was told that the fuel pump relay was built in the intelligent power box. If it stops running, I’ll post again.
Thank you for everyone’s help.

I’m sorry. Correction. The ECM ground wire.

It’s going back to Nissan. It shut off on me 3 times within 2 miles from the house this morning.

Car is still at Nissan. They can’t get it to stall. They said that it’s running without problem. Can I buy used ECM and replace it? Do I need ECM and key from the same car or just the ECM? Tia

The car is still at Nissan. I’m thinking of bringing the car back and trying to figure it out why it keeps dropping the power to fuel pump. Do you have a website that I can get the wiring harness diagram. Also the IPDM wiring. Tia

I guess I figured it out. I worked on it almost all day. Found out that it drops power at the IPDM (that was replaced with used one)
I ran on-off-on switch from the fuel pump up to the driver seat. Installed light on the ECM/IPDM side so I know when no power to fuel pump. Other wire ran from cigarette lighter to the 3way switch. Now when the light is off, I just flip switch to manual power. Light back on (ECM/IPDM) is working so I keep it on the normal working mode. So far, it’s been working fine. Tired of chasing ghosts. The car has only 33,000 miles on it, so I keep driving it as is.