I`ve seen the valve mentioned by 5er owners, but not TT owners, hence the 5er`s may be equipped with them, possibly because more folks full time in them? Just a guess.
2004 Chevy 2500HD Crew Cab 6.0l, 4.10r
2010 Jayco Jayflight 28BHS
Reese Strait Line with Dual Cam
P3 Brk controller