Yeah man sorry to hear. These threads pop up every now and again and I know limp mode is a SERIOUS issue! Anyone who has experience can tell you. I wish we could collect data in ONE PLACE (maybe limp mode sub section or ONE stickied thread Scott? lol) This way we could see who is experiencing the issue the most?
I find its the SRT guys the most and also some 3.7's which of course share the NAG1 A580 but also as Rob stated the shift module ESM has been the culprit for many. I had the issue few times when romping on it in the city and using the autostick. When I do not use it and leave in Drive it doesn't experience the symptoms leading me to believe it has ALOT to do with the electronics under the module having an issue and in turn sending false electrical signals to the pcm/tcm and thus leading it into "limp mode".
Mine even at times downshifted itself all the way to first at higher speeds but luckily I got her down quick so I didn't over-rev it and nothing serious happened. NEVER any CELS/codes, but once I even had entire dash wold flash few times and then stop after a restart. Then car would drive fine. TO NOTE: Had a Viper aftermarket alarm installed which I think was part of issue as one of module was going bad and after an update and new module, dash seemed a-ok!
I had a local trans shop plug her in to find NO CODES and no real issue driving around with the guy. I know the A580 is a strong trans so mechanically the tranny was NEVER my concern. As long as you keep maintenance up to date (fluid/filters etc) that isnt something ID worry about. The shift module is my main concern as it has little plastic pieces under it that work directly with the shifter when in autostick that can fail and also cause issue like "limp mode"
Really Id see when you experience it most and document it. Make sure all maintenance is ok and maybe have local friend/mechanic take a ride or peak and see if you can reproduce it. Beyond that, its really hit or miss with these things. You may never experience it again for rest of the vehicles life or may do it 1x a week in which case you'd need to solve it
G/L, I say we get a thread going and start collecting data!