Noticed after filling up my Bobcat s750 with Kubota v3800 that the power seemed to be "off". I didn't like the way the motor sounded either. It didn't sputter but it just sounded like it was missing (I'm at 500 hrs, all new filters, fluids) but rpms held steady. Just sounded "off" and the vibrations were different. Was running fine until I put 17 gallons diesel from my local gas station where I always get fuel. Here's what it does. When machine is moving, if I curl back the bucket or lift or hit the auxiliary circuit for my tilt tatch (when digging into a pile), the rpms drop significantly and it feels like a dog. The machine used to spill dirt over the top of the bucket before it started to stall. Last week I had it serviced and they did a computer update but supposedly it was only for the EH controls. For about 8 hours, it had tons of power and then after the fill up.. it was a dog. Could Bobcat have "detuned" my machine the way the Cat C series was? My tech didn't think so.. Had a service call and they checked fuel. No water or contaminants visible. Changed fuel filter again to be safe. Checked psi on fuel lift pump and it was within specs but it still ran like crap. Tech suggested I let it burn off fuel and then top off with fresh fuel. I did that and put another 17 or so gallons in. I felt like it ran good for about half the day, then back to being a dog when it hit half a tank. That was my perception. Anyone have a similar story? Could it be poor fuel? Any fixes other than draining tank? Additives? I have it on a job site and draining tank there would be a chore. I added some Lucas fuel conditioner yesterday but can't tell if it made a difference. Any help appreciated.