My brothers 1995 Chevy Silverado C/K 1500 stalls going into gear with the A/C on. With A/C off it can go into gear while stumbling as the RPM drops to about 250 before recovering. The load of the A/C just pushes it over the edge. In town with A/C on, every time the truck comes to a stop the motor stumbles for a few seconds at low revs, but so far has been able to recover without stalling. What could be causing this? It is the 5.7L V8 350ci with 127,000miles. It was handed down from dad at about 115,000 miles. Dad is infamous for infrequent oil changes.