ground circuit on 1995 gmc 1500 sierra

i have problem with 4.3 engine running after it starts up and runs for about half hour, i believe there is abreak somewhere in the ground circuit i added a new ground strap from battery to block where else should i try adding new ground circuit because i feel when driving ignition seems to cut out, then when you let it sit for afew minites it restarts till problem happens all over again