Hello everyone I have a 1997 Suburban that's giving me a fit. Generally can diagnose anything but after thinking for a few weeks and trying a few things I'm interested to hear some ideas outside the box. Truck only has 120k original miles. The issue I have is when it warms up and goes into closed loop (converter locks up) I get a stumble of I modulate the throttle and stay in lock up. For example cruising 60 mph.. lightly press the throttle to accelerate while keeping the converter locked..truck will make a single "buck" like you turned the key off and on really quick. Also if you are steady accelerating with the converter locked and then quickly back off the throttle it will give the same "buck". Wide open throttle runs great. All other times it runs great. Starts right up immediately cold or hot. No codes currently but did have a cat monitor O2 heater code previously. I have done a full tune up with quality parts, replaced the EGR, and verified cam retard at -1*. When I checked the cam retard I was excited to find it at 12* and thought I found my issue. I reset the cam retard to -1* with my snap-on scanner hoping that was my problem but it remains. I don't believe it's a fuel issue because of the violent nature of the stumble. It definitely feels electrical/ignition. I have also monitored the crank sensor with the scanner and don't see any drops. TCC slip rpm also doesn't really seem to jump around during the stumble. I really don't want to throw parts at this thing. Thanks for any ideas.