I have a titan on my 15, I did a fass 165 and fass sump at the same time. I put the sump right under the sending unit and drilled holes in the sending unit cup and cut the bottom 1/8” off to make sure the fuel got into the sump without problem. The sending unit cup sits on top of the bolts in the sump as well so fuel has free roam over the sump without restriction. It happened this way and the factory tank calibration is actually pretty close gauge wise, just on the dash the miles to empty is off but that never bothered me anyways. I regret doing the titan tank and sump. With anything less then 1/4 tank when you slow down the fass looses prime when the fuel sloshes to the front of the tank. Ive yet to have the truck stall out as I try not to get below 1/4 tank, but seeing the fass pressure gauge drop to .2-.6 psi sure makes you nervous. I didn’t gain the extra 24 gallons or so, I may have gained 10-15 at most because at 1/4 tank I put in aprox 38 gallons. Just above 1/8 tank the fass starts changing sound and I’m able to squeak in 43 gallons but you’re basically running on hopes and dreams at that point. Hind sight I should have done the fass 95 made for the lml trucks and no sump with the titan tank and maybe I’d be able to use more of the 58 gallons I paid for. Food for thought on what to do and not to do.