GMC Repair: 1994 gmc yukon, gmc yukon, spending money

Question
im trying to set the timing on my 94 gmc yukon 5.7L. and my single wire electronic spark timing connector below the glove box ,seems to  set  my timing off  once i hook it back up, ive done just as the manual says and am wondering if maybe the ecm is bad ,  

Answer
Hi
Are you getting any service engine soon light?
I would suspect the Ignition module inside the Distributor before I say it is the ECM because the ECM gets its ignition data from the ICM.
While the set timing connector is unplugged, set timing to 0*.
Then replug in connector.
If it looses the timing, I'd think the ICM mak be at fault.
If unsure, I'd take it to a repair shop in your area your familiar with and get them to diagnose before spending money on unnecessary parts.
JUST advice from experience
Hope it helps
Good Luck
Paul