GM-GMC: 1992 chevy c2500 no power under load, vacuum leaks, engine vacuum

Question
I have a 92 chevy 2500 w/350 and tbi.the truck has no power under a load, as in passing or pulling out.No codes stored in comp. Fuel pressure is steady 14pnds.under all conditions,while driving.Timing is set at 0, with spout disconnected.No vacuum leaks. good engine vacuum at idle."20inches".New catalytic conv.,exhaust is not plugged.With a timing light on it the engine advances the timing and will suddenly pull the advance at about half throttle.It has a new module in the dist. You cannot hear any pinging or engine noise and no code 43.Comp says no codes found when scanned. Could this be a bad distributor or could the electronic spark control module be faulty. Paid for 3 hours at a mechanics and still no solution. Any help would be great. Thanks for your time.

Answer
It sounds like you have a distributor problem.  Swap the distributor with a known good distributor out of a truck you know works properly.You seem to be handy with a timing light so I won't hesitate to have you remove the distributor.  If the problem disappears, the distributor is faulty, disassemble it COMPLETELY.  Check for very small cracks on the base or in any of the components.  I have seen this on trucks with similar concerns that I exhausted all other resources on.  Look very very carefully.  If the problem persists with the new used distributor. Hmmm.  Get back to me and I will have to think about it somemore.
Hope this helps, sorry for the slow response.