Your truck will do well towing that load. I certainly would be more comfortable keeping that truck if I were you vs rolling the dice and buying something else that is used - especially if you are thinking of going with a half ton.
The exhaust brake is a nice feature. With your load, it is NOT a mandatory one. So, if the budget is an issue, skip it. Your truck is perfectly safe and capable to tow the load you are contemplating in stock form.
On my 03, I had a Jacobs brand put on, and it worked very well. Was a great addition to the truck, but I was towing more weight and wasn't really concerned about budget for that. If you look at other options, I would consider the Jacobs - but I would buy it through your local Cummins (not Dodge/Ram) dealer, as it will be significantly less $.