I've read my Chevy truck manual from cover to cover several times now and it talks about the Regen happening. Says it's suppose to do it at certain speeds, and after so long, yadda, yadda, yadda. It warns about driving too slow and regin not occuring correct or pre-empting it by stopping the engine.
OK, I've had my Duramax Diesel for 4 years now, and never ONCE noticed anything ever occurring. I keep waiting to feel something, loss of power, rev-ing engine, anything... nope. It does it so slick I never noticed or felt anything happening.
For all I know, it could be regenerating every 100 miles? This is one of those "things" I just never understood about my truck. It drives fantastic, no complaints, and tows like a monster! Wonderful truck, just can't say how often mine does that? I have no clue.