1990 Silverado 5.3L w/AT ignition timing
 

I need to order a new VECI label for my truck, but in meantime, I was wondering -- What is the ignition timing suppose to be set at for this vehicle?Looking through previous posts, it appears like it is supposed to be 0 degrees BTDC with the electronic spark timing (EST) bypassed, but at what engine rpm?

According to my timing light, the engine currently idles at 620-650 RPM, and my timing is set at -1 deg BTDC (i.e. 1 deg AFTER TDC) I plan to adjust it correctly, but how critical is it to set the timing spot on?You'd think the computer would just compensate for an additional degree after you re-enable the EST.

I'm not having any driveability problems with it. Was just getting ready to do some routine maintenance on it and realized I'd never checked the timing before, so thought I'd do that as a baseline.