Here is what I have : 96 7.3 auto 2wd. I changed the fluid 2 times on this truck. It currently has mobil 1 full synthetic atf in it. My speedo would bounce a couple mph 55-60 so I changed it with a used one from ebay. Still bounces the same. Not sure if thats an issue or not. This truck will have a vibration once i get into 4th gear. It will do in with overdrive off or on. Its like a pulse, pause with no vibe, pulse, pause with no vibe. Imagine if you are counting, on every even number it pulses a shudder/vibration then every odd number its fine. This started not long after i put a php hydra tuner on the truck with it on 40 hp tow. I have tried it in stock form and it still does it. Any ideas on what I should do next?