I have a 94 Z28 that is all stock. When it gets warm, it starts to stumble at lower RPMs. (1000-2200) also, the cooling fans never come on, so when i drive for about 15 minutes or so, the temp goes to 260+ degrees. It has a new opti, new plugs and wires, fuel filter, and the correct 50/50 antifreeze. when its cold, it runs great. Above 2200 rpms it runs great. any help on this would be greatly appreciated, although this seems to be a common problem with no solution.