[FED 387]

If Im not mistaken doesn't the main vehicle electrical power come from the positive post on the starter?? If so might check the cable coming off that post and the terminal end too----as old as that truck is over the years between vibration heat and the weather that lug may have deteriorated---also are the replacement starters GM look a likes (offshore knockoffs) or are they either new or rebuilt BY GM/AC- DELCO starters?some of that crap does not have a very long life to it---also check the body grounds for good contact with the frame--FED 387