Hi Howard, just reading your posts and diagnosis of the poor hot running on your GTA, did you ever get a resolve?
My V6 Turbo is having an identical issue, I have replaced both fuel pumps, filters, replaced the coolant temp sensor - readaing 280-370ohms (cold to hot).
I've yet to check/replace the fuel pressure regulator - but the fault happened very suddenly, OK one day - poor hot running and no idle the next! However the car runs fine when cold until warm...