2004 GMC Sierra Will flashing computer erase an Edge progra

No. Reflashing installs updates and cleans up unnecessary used space in the computers memory so it can work better. Further more, every time a vehicles' computer is reflashed now-a-days, there is a code that sets the time - day - and year that the computer was reflashed. This code is non-eraseable. The settings from any date before the reflashing occured can always be observed, but not reset.
Did you check for vaccume leaks?

To add to pear69's info here is something to read and think about:Caution: Customers should be informed that even after the calibration has been returned to a GM certified configuration, it is likely that engine, transmission, transfer case and/or other driveline components were weakened to the point of premature failure while subjected to the higher stresses from the non-GM calibration (Power-Up Kit). Engine, transmission, transfer case and/or other driveline components where a non-GM engine calibration has been verified are not covered under the terms of the New Vehicle Warranty. An Engine Control Module (ECM) algorithm was implemented that records the engine calibration part number and Calibration Verification Number (CVN) for the last 10 flash programming events. The ECM only records the engine calibration part number because it contains the parameters for increasing torque and fueling rates.

Some customers may have re-programmed the ECM with a non-GM released calibration. The (Power-Up Kit) powertrain calibration changes fueling and timing parameters and likely contributes to the following vehicle conditions:

"Â Poor Performance

"Â Black Smoke (This symptom is not valid for the 6.6L (LMM) diesel equipped with the diesel particulate filter (DPF). The DPF will trap black smoke unless the DPF is cracked, melted or has been removed from the exhaust system.)

"Â Knocking Noise

"Â Engine Damage
If a vehicle comes in for service for a driveability/powertrain concern as a result of a Power-Up Kit installation, the dealership technician now can read the last 10 engine calibration part numbers and CVN history using a Tech 2 Â.

The dealership technician would input each ECM calibration part number into the SPS/TIS2WEB CVN database to confirm the CVN history information.
To make a long story short, power programmers do more damage than improve.I've never had to go throught this working at the dealer but I have seen other horror stories from programmers on these diesels. GM started this years ago. Just my 2 cents.

Yall best read brian 1s' answer again. I reckon the edge juice with attitude programmer is reckin that truck of yours.