I had originally wanted a Titan or some sort of factory replacement tank. But wow, those are expensive. I ended up with an in the bed 40 gal tank, complete with elect pump, filter, hose, and nozzle for $150 off from Craigs list. I lose 8 inches out of the front of the bed, but for the cost savings, I can live with that.
2008 Duramax/Allison LT2 Crew cab Standard Box. Hellwig Air Assist. BD Diesel VVT Turbo Brake. 2003 Coachmen Chaparral 295 IKS
The computer doesn't have to be re-calibrated with the replacement tank that I have. It uses the original OEM sending unit. The only thing that isn't correct after the switch to the bigger tank is the range to empty number. Since the computer still think I have a 26 gallon tank and now I have 52, it is pretty easy for me to multiply by 2 in my head. All other numbers are correct.
I have been told that to change the tank size in the computer it requires a re-flash. GM can and has interpreted this re-flash as a reason to void power train warranty. Just a thought.
Adding extra fuel capacity was one of the first improvements I made to my truck, and I don't regret it one bit.
An average driving day for me is about 300 miles, and I did not like being on/near empty as I neared the days destination.
I decided that I wanted a cushion of an extra 10 gallons of fuel at the end of a driving day. For me, that meant I needed to have 45 gallons of fuel total. I think that would have worked for me.
However, tank prices being what they are, what I ended up with was a gravity fed, 50 gal. in bed, tool box/ fuel tank combo, that I can drive as many hours as I want, and refill when I want to, with a total of 80 some gallons of fuel.
It took one of the driving concerns right off the table on our two cross country trips.
Still, I think the main concern is being near empty at the end of your driving day, so stay away from 30 gallons of fuel. Whatever cushion of fuel you think you would need should determine your choice of tank.
I don't have an extra fuel tank on my trucks, but if I were to go with a fuel tank, it would be a higher volume replacement tank for the front/mid-ship factory tank. No way I could ever give up any bed space for an aux fuel tank. I use all the bed space I have in all my trucks for hauling things.
One other thing to consider is the tank construction for the replacement tank. The TransferFlow website says the shipping weight is 230lbs for their tank. Their tanks are made from aluminized steel. The Titan is a polyethylene, like the stock tank and weighs in at about 45-50 lbs. including brackets. That is a pretty substantial difference.