96 Z71 service engine light, but NO CODES?

I have a 96' Z71 W/@150,000 miles, Runs great,good mileage, excellent maintenance, but the service engine light stays on, the local mechanics are stumped. There are no codes and all the engine and electronic parameters are good when hooked up to the diagnostic computer. One mech says bad computer, but it runs and checks out fine.(Still runs like a scared a@# ape under all conditions) the truck DOES have an GM remanufactured computer that was installed in a recall and carries the "updated wiring harness" tags that so many of the first Vortecs have. I can't see repacing the comp if the truck is running and no codes. Any Ideas would be appreciated.
(i've already put in new wires, plugs, rotor, cap, MAF, O2 sensors, which all check out fine.)
Thanks, TR
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did the mechanics check out any updated TSB's for that condition? I'm a technition also, and thats where I find lots of those wierd conditions.

Nick

I'll check with my tech and see if he's found anything, he's recommending a call in troubleshooting service, but the calls are like $40.
I would hate to pay for information I should be able to get for free.