Not sure if I'm a day late and a dollar short....
I had a similar problem....I replaced the knock sensor in my pick up and verified timing and it seemed to solve the problem.
Not sure what the problem is but maybe a short somewhere? Trace the plug wires for the speed sensor maybe they need replacing.
Also check your grounds...I was having weird electrical issues and I literally went and replaced EVERY ground cable and when I pulled the old ones off I cleaned the...