Time to put this one to bed once and for all--finally. I was in the process of selling the '99 in question when the excessively hot temps brought the rumble back. I followed Hako's sound advice and hooked up the gauges again. This time in the proper weather conditions. Only when the temps are around 100 Fahrenheit (32+Celsius) did the discharge pressure of the compressor hit the high pressure cutout, the clutch disengaged, then repeated. I recovered refrigerant enough to keep the pressures in the normal rangs and the problem was solved. I would recommend in hotter climates, the charge be kept at or on the lower side of the 700 +or- 50 gram range. I weighed in 700+20. Not good. Thanks to all who chimed in.