Hi,
 
I ended up changing just about everything and after a new ecu, fuel pressure sensor, fuel pump driver module and three fuel pumps I gave up and took the car to an auto electrician. They had the car for quite a while and eventually we decided to try another pump in the car and it worked.. I drove the car for about 500kms with no issues. By that time I had decided it was time to move on so I traded it for a Falcon.
 
I have a feeling that the issue was to do with the fuel pump driver module which was worth stuff all to buy. I think it was playing up and burning out the pump.. it was the only logical explanation I could come up with.
 
Where are you located?
 
Cheers,
 
Damion

Am in Sydney and having similar issues, although not very often - maybe once a week and fine next time car driven.  Currently doing over 400kms a week.
 
Latest yesterday, taking off on a hill and was over half a tank of fuel, sluggish all the way home and then this morning all fine
 
Anyone on top of this that can be recommended to have a look at my ST170??
 
Thanks in advance 
 
Regards Alex