1996 GMC ENVOY Fuel System Other Problems

HELLO, WE PURCHASED THE 2006 YUKON DENALI ENVOY WITH LOW MILEAGE BETWEEN 30,000 ' 45,000 MILES. WE DIDN'T EXPECT TO RUN INTO MAJOR ( THROTTLE BODY AND FUEL SENSOR'TANK EMBEDDED) PROBLEMS. THERE ARE MANY COMPLAINTS LODGED ON THE INTERNET ABOUT THESE DTC ENGINE TROUBLE CODES (P2135, P0463). THE SUDDEN LOSS OF POWER IN THE MIDDLE OF TRAFFIC MAY CAUSE AN ACCIDENT. ACCORDING TO GMC TECHNICAL SERVICE BULLETINS IN CORRECTING THE PROBLEM, THE FIRST DEALER TOLD ME THEY MUST FOLLOW A DIAGNOSTIC TROUBLESHOOTING FLOW CHART TO RESOLUTION. THE FIRST GM/GMC DEALER STATED THE FIRST STAGE OF THE DIAGNOSTIC FLOWCHART SAYS THE THROTTLE BODY SHOULD BE CLEANED AND NOT REPLACED. THE REASON NOT INITIALLY REPLACED IS BECAUSE THE THROTTLE BODY IS A HIGH PRICED ITEM. WE THEN TOOK IT BACK TO THE 1ST DEALER AT WHICH THE DIAGNOSTICAL FLOWCHART WAS AGAIN USED. ACCORDING TO THE FLOWCHART THE NEXT COURSE OF ACTION CALLS...