2000 Silverado 2500 6 ltr

This issue has stumped every mechanic who has tried to figure it out.

My truck's idle falls to the point it occasionally dies, if it does not die, it bounces between normal idle and stalling.

This only happens when the transmission is cold and the truck is in gear. Once the transmission warms up the problem goes away completely. The problem also does not happen in park or neutral, only when in gear.

I have replaced every sensor there is as well as the fuel pump. I am not throwing any codes.

I have let the engine warm to operating temperature and the problem still presents itself. I have to drive the truck to warm up the transmission. Once the trans temp needle starts to move, the idle problem disappears completely. I drove it from California to Oklahoma without one problem once the transmission warmed up.

Any ideas? It makes no sense to me, but I am a novice.

Thanks all!