Can never have too much truck, especially given the Class 5 rigs are no bigger than duallies and still a pickup body. Only downside with the 01 F-550 is no wide track front axle and it's 8 vs 10 lug iirc, but the rest of the frame is the same as with the new one.
I'd say buy it then change all fluids: diff, automatic, power steering, brake and oil plus filters.
Get the auto checked out but if you can get it for 9 even then it's a decent deal.
Agreed re 3/4 tons, not much payload there.
05 Ram 3500 SRW QCSB Laramie 4x4 Cummins, 610lbs, 23k GC, 9.9k GV
(totaled) 16 Ram 3500 SRW RCLB SLT 4X4 Cummins Aisin, 900lbs, 25.3k GC, 11.5k GV
06 F550 4x4 PSD, 570lbs, 33k GC, 19.5k GV