I wouldn't worry about either of the readings you have. The HPR's are all over the map. I have seen them with pressures as low as 80 p.s.i. static at the test port and the car runs fine. The range for the 1st stage of the LPR is 2-4 p.s.i. so 3 p.s.i. is right in the middle. The 15 p.s.i. drop you see is most likely line pressure drop between the HPR and the test port when you are asking for high fuel flow when the engine is loaded. This would verify that the inlet filter in the HPR is not restricting fuel flow. The 3 p.s.i. reading at the 1st stage test port verifies the low pressure lockoff valve and the 1st stage of the regulator is working correctly. The only thing left to check in the regulator circuit is a monometer check of the second stage of the LPR. Beyond that, what does the car do when it is running so-so on CNG I re-read all of your earlier posts and since your last one was in September, I was wondering which of the original problems are still with you.