So out of nowhere my truck decided it would switch to limp mode (my guess). No warning lights and no codes stored in the OBDII system. After searching I found the likely cause was the 1-2 shift solenoid, so I dropped the pan and swapped 1-2 and 3-4 solenoids and filter, buttoned up, and refilled with fresh fluid. Test drive revealed no change. I'll try to reset the computer by removing the ground cable for 30 minutes. If that doesn't do it, I'm going to unplug the harness from the trans and try to diagnose and clean the connections. Any suggestions?