Cpmputer replacement.

[302Z28]

For the past two months, I have been replacing parts trying to cure a rough idle - hesitation problem. Yesterday, two codes were stored (0172 - fuel rich left bank, 404 -EGR valve) A shop diagnosed the issue and stated that the PCM computer needs replaced. Cost between $400 and $600, plus $75 for flashing. I can buy a refurbished unit at Schucks for around $100, but it will need to be flashed. I have been told that only a dealership can do this. This computer fits several GM cars, so can any GM dealership do the flashing? I'm not exactly fond of the local Chevy dealer.

Any advice on replacing a computer?

Thanks for any help.