I have no idea what the 4000 costs. Add that to the cost of a disk brake kit. Now how much more is it to just get the 7, 8 or even 9k IS???
As mentioned NOTHING out there even comes close in ride quality, serviceability and longevity.
Unit on left is 9K and other two are 8K.
2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
37,800# GCVWR "Towing Beast"
"HeavyWeight" B&W RVK3600
2016 MobileSuites 39TKSB3 highly "Elited" In the stable
2007.5 Mobile Suites 36 SB3 29,000# Combined SOLD