95 ecsb 2wd 5.7 4l60e. Truck does one of three things. It runs fine for days. Or i will start it and it goes nuts idling at 1300 with the iac stuck wide open. It also locks the trans in 3rd gear. I can manually pull it into first and then shift to third but no second or overdrive. The other thing it has done twice now is while driving normally, it will suddenly drop into third gear. Ill pull over and it will sit and hunt for an idle between 900 to 1100 with a normal rythm. Again the same condition with the transmission. Check engine light is on steady in both cases. Also when this happens, it will not go into diagnostic mode with a paperclip. I can't predict when its going to happen. It has nothing to do with hot or cold starts. And it fixes itself everytime. The CEL will go out and then its fine. Once that happens I can pull the codes. It throws one for everything on the list of codes. So my immediate thought was bad grounds. Cleaned those thoroughly. Still does it. This has been going on for 2 weeks. I cant force it to fail and i also cant get it to run right. It just fixes itself. Ignition switch maybe? My only concern there is its not exhibiting the common symptom of a screwy gauge cluster or prndl. If the ecm was bad it would just be bad right? Im pulling my hair out. Its my DD and i drive 100 miles round trip every day for work. Thats a long way to be stuck in limp mode when it acts up.