I am 54, and just bought my first diesel truck. 2007 Chevrolet Silverado 2500HD 4X4 New body style 6.6l LMM. I am having the DPF removed, and an external fuel pump added. I'm not looking to go crazy with horsepower, I just would like recommendations on upgrading. For example, transmission cooler, etc. I plan on using it for mostly pulling campers, and trailers.

2 pulleys I have here 56mm OD don't have the right spacer, them are 9mm, and the right distance is 6.5mm
it is essential to have the right distance, in order not to wear out the belt