The exhaust has a flap control but you are right, the dealer told me that once you get used to it, you drive it with the flaps open most of the time. I really put a lot of pressure on the dealer to get the exhaust ready for my pickup, it wasn't easy (the exhaust is hand made). Almost got him to do that 7.3 l tuning on my engine too but I just couldn't do it...lots of money (20k) and the car is fast enough (hopefully). It makes more sense to wait for that supercharged monster successor.
I was thinking about a cold air intake mod (instead of the current air filter box) but dealer advised against it, he said that the exhaust is already very loud, the louder suction sound would not really be heard and the cold air intake can create problems because of the very hot engine. Since the dealer has a lot of experience with tuning, I trust him.
There are a few ECU mods he can do (more aggressive shifting, even better throttle response and a couple of optimizations which would require at least 98 octane fuel), cost is around 1200 EUR as far as I remember but I'm not a friend of ECU mods on a N/A car, so I won't do it. The dealer's chief mechanic told me however that the SRT ECU is quite adaptive, even to higher fuel qualities, so using VPower could actually improve performance (I am going to find out if this is true).
Regarding the sound of the exhaust: People actually expect this from a true US SUV, so I wouldn't worry too much about the exhaust being too loud.
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RC (Germany) - Rennteam Editor Porsche 991 Turbo S, Porsche Boxster S (981), Jeep Grand Cherokee SRT (2014), BMW X3 35d (2013)