This is absolutely incorrect.
80mg of omeprazole is indicated in treatment resistant gastritis, GERD and gastric ulcers.
80mg of omeprazole divided into twice daily 40mg doses is superior to 40mg once daily in treatment resistant conditions.
Many people don't achieve full acid suppression with 40mg once daily.
Here is a study to support these claims. http://www.ncbi.nlm.nih.gov/pubmed/8759655
I see from above that you have been given different opinions by two American doctors.
I am a UK doctor and very familiar with prescribing omeprazole.
Basically both your consultant and your GP are right!
The standard dose of omeprazole used in the UK is 20mg to 40mg daily.
However if your symptoms are worsening or more troublesome (and from what you detail above yours are) many specialists now recommend a temporary increase to 80mg daily (often taken as 40mg twice a day.) You say your consultant wants you to do this for 3 months which is common.
I had to query this myself only recently when a family member was told to take a higher dose, like you, for a while as I did not know some specialists were now doing this.
Hopefully your consultant will write to your GP explaining why he or she wants you to take the higher dose for a while.
Hope this helps, Best wishes.
I am a caring and compassionate UK doctor and have been qualified for 23 years. I have widespread experience in GP and cancer care.