Engine brake on 2013 3500 Dually
 

I just bought a 2013 Dually with the 6.7 cummins. . I own and use a 2013 2500 6.7 cummins for camper. My question is why does the engine brake work better on the 2500?
When i use the engine brake on 3500 it sounds weaker and does not seem to slow me down at all. The light is on dash as yellow than green when i push button again so it looks like it is being activated.
Is there a fuse or relay that I cant see in fuse box?