Hi John,

What system is this vehicle running?

The high duty cycle/amps draw would lead me to look into the following;

Either a poor low pressure supply,(the pump cannot generate pressure without a good supply) Can you/have you already checked the low pressure system using Vacuum/pressure gauges?

A high pressure leak,(you will struggle to generate pressure in a system that is not sealed) I know you have carried out a leak back test, but under what conditions?

Or a under performing high pressure pump.

Have you a sealed rail test kit?

HTH

Regards Mark