Sorry I missed your mention, and that’s a tough question.
I like banks a lot because they are well proven for diesel performance. They even build their own diesel crate engines. They claim their safety monitoring of engine and trans parameters or more stringent then the stock engine monitoring. I believe them based on their history. The Derringer works very well, and I can monitor it pulling power if there’s trans slippage (through our shop’s snap-on scantool).
I like almost everything about the tuner. Banks has weathered a lot of storms, so I’m not worried about them going out of business- i.e., support will be there for you in the future.
The two things I don’t like about it:
1) it does nothing for the EGR system
2) it does not increase gas mileage at all, when there is plenty of opportunity to do so.
GDE has a much shorter history, but if they were messing up tunes and blowing up engines or transmissions, the internet would be blowing up about it. That’s not the case, so I think they’re fine.
The things I don’t like about GDE’s tunes:
1) It’s a PITA to get the tune done unless you drive there. You have to be willing to have at least three days (realistically, a week in case of shipping issues) of truck downtime while you ship out the PCM to be flashed. He won’t be offering a handheld for a while. (He told me ~4 years when I talked to him on the phone this past April)
2) If you don’t what truck downtime, you need to order a spare PCM and have it cloned at a dealer that will do it for you. GDE can clone, but you have to send your truck’s PCM and the spare PCM to them at the same time, defeating the whole zero downtime thing.
3) If GDE decides to close shop tomorrow, you’re out of luck on support or updates. I have faith they’ll weather economic storms though, as their overhead is pretty low and they can still operate by renting dynos and do the rest from an office in the owner’s house if they really wanted to.
4) Price is pretty high for a canned tune.
Things I love about the GDE tune:
1) Increased mpg.
2) Makes better use of the low-pressure EGR loop to reduce soot buildup in the intake.
3) Engine braking.
4) Trans tune included.
All that being said, I think GDE wins because of the reduced soot and the gas mileage increase. I would 100% put it on a spare PCM though. If something were to happen, I’d want a quick fix from putting the stock PCM back in while I figure out what went wrong.