i have a ctd 2500 with a nv5600 tranny. is there a easy way to figure out what gears i have 3.73 or 4.10?

 

Look in the glove compartment, there should be a label with all the invo and accessories, incuding gear ration and if LS or not. They also had it on near the hood latch on the hood itself (look up when you open it).

Otherwise crawl under rear end and look the tag bolted on differential