Well, it's happened. If you mod your PCM, you have just invalidated your warranty!

See the excerpt from the PDF Below:

"#09-06-04-026: Identifying Non-GM (Aftermarket)
Engine and Transmission Calibrations for V8 Gas
Engines - (May 18, 2009)
Subject: Identifying Non-GM (Aftermarket) Engine and Transmission
Calibrations for V8 Gas Engines
Models: 2006-2009 GM Passenger Cars and Light Duty Trucks
(Excluding Saab 9-7X)
2006-2009 HUMMER H2, H3
Equipped with V8 Gas Powered Engines Only
Attention: This bulletin applies to V8 gas powered engines ONLY. For all other gas
powered engine applications, refer to Corporate Bulletin Number
08-06-04-033D. For diesel powered engines, refer to Corporate Bulletin
Number 08-06-04-006C.
General Motors is identifying an increasing number of engine, transmission and catalytic converter
part failures that are the result of non-GM (aftermarket) engine and transmission control
calibrations being used.
When alteration to the GM-released engine or transmission control calibrations occurs, it subjects
powertrain and driveline components (engine , transmission, transfer case, driveshaft and rear axle)
to stresses that were not tested by General Motors. It is because of these unknown stresses, and the
potential to alter reliability, durability and emissions performance, that GM has adopted a policy to
cancel any remaining warranty coverage to the powertrain and driveline components whenever the
presence of a non-GM (aftermarket) calibration is confirmed - even if the non-GM control module
calibration is subsequently removed.
Warranty coverage is based on the equipment and calibrations that were released on the vehicle at
time of sale, or subsequently updated by GM. That’s because GM testing and validation matches the
calibration to a host of criteria that is essential to assure reliability, durability and emissions
performance over the life of the warranty coverage and beyond. Stresses resulting from calibrations
different than those tested and released by GM can damage or weaken components, leading to poor
performance and or shortened life.
Additionally, non-GM (aftermarket) issued engine control modifications often do not meet the same
emissions performance standards as GM issued calibrations. Depending on state statutes, individuals
who install engine control module calibrations that put the vehicle outside the parameters of
emissions certification standards may be subject to fines and/or penalties.
This bulletin outlines a procedure to identify the presence of non-GM (aftermarket) calibrations. GM
recommends performing this check whenever a hard part failure is seen on internal engine or
transmission components, or before an engine assembly or transmission assembly is being replaced
under warranty. It is also recommended that the engine calibration verification procedure be
performed whenever diagnostics indicate that catalytic converter replacement is indicated.
In May 2009, the PQC will begin piloting a process to confirm the ECM/PCM calibration is GM issued.
Beginning on May 18, 2009, the PQC will require a picture of the engine calibration verification
screen, as outlined in this bulletin, before authorizing any V8 gas powered engine replacement.
If a non-GM calibration is found and verification has taken place through GM, the remaining
powertrain and driveline warranty will be cancelled and notated in GMVIS and the dealership will be
notified.