My '94 LT1 runs smooth for the first 50 miles until engine temp gets hot. When it is hot and I am in stop and go traffic with the A/C on,engine surges and sometimes runs rough. At that point, engine hesitates, surges and pings when accelerating. Any ideas what is causing this? No codes showing up. Is it the optispark? Would really appreciate any ideas to correct the problem because I love my 'vette. I is my second in 11 years of vette ownership. Thanks!