Gas won't flow from 2nd tank

Actually it does flow sometimes, sometimes not at all or sometimes with low pressure. My setup has two 30# tanks, one on each side. On the curb side there is a main auto changeover valve and regulator. The road side has the other tank and a secondary regulator. I'm on the third secondary regulator. When the new one's have been installed and tested they worked alright. But after awhile I'll turn on the stove and get nothing or very low flame. In a couple of hours it may be normal again. I use the gas side of the hot water heater and it may be on or not when pressure drops. I now keep the roadside bottle turned off and when the other bottle is empty switch bottles. Three service dealers have not been able to find the problem. Maybe someone on the forum has had a similar problem, unless all three secondary regulators have been bad.

Thanks,