Bootloader Timeout/Fail.

I came across something that I thought everybody should know on my personal vehicle. I have a 2005 Silverado 1500 5.3 with an aftermarket radio. I got tired of losing my radio settings, so I ran a switch inline of the Class 2 Data Line. I have flashed it multiple times with no issues, using the MPVI2. I recently replaced the HVAC module (manual controls), for the 2nd time. Once for motor control fault and this time for intermittent A/C signal failures with one that I got from NAPA (some different hardware to prevent common failures). I then fought the Bootloader Timeout issues reading/writing, until I remembered that I replaced the HVAC module. I removed the I/P HVAC1 (HVAC ignition) fuse and had no issues writing. Just a reminder that aftermarket radios aren't the only thing that can cause issues.