We used Dewalts exclusively from 2005-2009. (And built our own completely custom shifters prior to 2005.)
In 2010 we made the decision to take the weight penalty and use the completely COTS AM Supershifter components....to make a long story short, we had lots of problems with our Dewalt setup in 2008.
We were constantly liquefying the guts of the transmission itself. My theory is that we had gotten to a truly rigid setup where the loads from the wheel on the carpet traveling back up the direct drive shaft were just too much for the transmission to handle. (Prior to this we had chains and other load absorbers in the loop) I cannot recount every modification that we made, but it's safe to say that by the end of 2008 we had more or less re-designed/re-built the entire Dewalt assembly.
In 2009 we debuted a version of the Dewalt based on their 36v drill transmission.
36v Dewalt Trans in MuleBot This setup survived 2009 for obvious reasons (regolith), but started to show signs of weakness by the start of 2010.
Somewhere in this evolution we decided to accept the small weight penalty of using an AM Supershifter over the stress of building completely custom assemblies.....to date we have never had a failure or open issue with the AM components. FYI...we are one of the rare teams that servo shifts! I believe it works flawlessly, though Andymark states on their website that servo shift is inferior....it deserves a second look.
All of this aside, we still use Dewalt transmissions all over our robots. They are super light, easy to implement and have handy built-in clutches that make them friendly to use for all sorts of scenarios.