RPO DEFINITIONS V V I 9 I I I I JB3 BRAKE POWER DISC DRUM 4600 LBS JB5 BRAKE POWER DISC DRUM 6400 LBS I Y JB6 BRAKE POWER DISC DRUM 7200 LBS 1 JB7 BRAKE POWER DISC DRUM 8400 LBS 2 JD5 BRAKE DUAL POWER DISC DRUM 6400 LBS A JD7 BRAKE HYD POWER DISC DRUM 8400 LBS I V I I I V I q 1991 GENERAL MOTORS SERVICE PARTSOPERATIONS L1 TRUCI e 526 A 14 000 GROUP V8 4 92 V 1 91