Just bought an 02 2500 HD and have question

[LT1 Burb]

Hey guys, I usually hang out at the 60-66 forum but I just bought an 02 Silverado 2500 HD with a 6 litre and auto. It has 103K on it and seems to be a pretty nice truck. It had a rear caliper sticking so I changed all 4 and brakes work great now. Question, I am using this to tow my car trailer and need to know what is the best brake controller to get that is plug and play. Also what is the best bang for the buck improvement for power and mileage. I just checked and I am getting 13MPG. Is a catback system worth the money, cold air kit etc. ANy help would be great.