Local Mechanics Unsure - 2003 Toyota 4Runner V8.

I purchased a 2003 4Runner that was primarily serviced by Toyota for its lifetime.

It's ~350,000KM. Since purchasing I replaced the timing belt, battery, and installed a new head unit.

It started having troubles turning over. There was a grinding noise. Mechanics told me it was a fuel pump issue and have since replaced it, but it's still having issues starting smoothly consistently. It's 50/50 whether it'll start. I'm able to get it to start by applying the gas pedal and raising the RPM.

My mechanics are unsure what is and think it might be an electrical / computer issue?

Check engine light isn't on, and they're not getting any codes.

Any advice would be very helpful!

Thank you!