Hey everyone I need some input. I bought a 88 Sierra to fix up for my stepson and I am having some issues with it. The truck starts good and runs good when it’s cold but once it warms up it stumbles and will stall at an idle. I have changed the temp sensor because it was bad I also replaced injectors because they were junk. I have replaced the engine to frame ground because that was another previous issue. I have looked it all over there are no vacuum leaks that I can hear or test by spraying starting fluid. The engine was completely rebuilt 30k ago with new cam and my friend I got it from drive it with no issues. I have found that when you apply the brake the engine dies down and idles up after you release the brake.

My left trailer light illuminates properly when indicator and/or brakes applied, however dies not illuminate when headlights are on. The Right eorks fine. The trailer lights are LED (probably 20 or 30 LED’s in each)! Any idea how to trouble shoot? thanks!