I know the Big Horn and the Landmark use the 1621HD I think the Toyhaulers are the same. When I bought my TrailAir FlexAir pinbox they told me that they discontinued the Tri-glide and replaced it with the FlexAir. They had a lot of failures with the Tri-Glide.
Dave if yours is actually leaking drain the air out and pull the air stem out and reseal the threads, It worked on mine.
If you don't change anything in you loading from when left home to when you came back,the air bag will be the same. This is not usually the case especially when dry camping. on your way out your fresh tank is full (behind the axles) gray and black are empty. Coming home Your fresh tank is empty and your gray and black tanks are full. Moving all of that weight forward, which compresses the air bag more.