Those Optisparks sucked when they got hot, wet, old, or if you looked at it funny, they act up. An Optispark would be the whole distributor. OBD-2 started showing up on some 1995 model year cars. It really sounds like you may want to bring to a Chevy Dealership. If you think it is the computer I would trace all wires ohm them out, check voltages, make sure nothing is broken.