94 suburban with 6395 pcm, stock drac and stock speedo. When I start off first drive of the day at about 15 mph the speedo goes full right and then back to normal. At about 40 mph steady state, if I lightly tap the gas ( 5 in vacuum change ) the speedo will go up 5 mph and come right back down as pedal down. It shifts as it should and goes from idle ve and spark at 3 mph as it should so I don't think it is a vss problem. I have reseated the plugs on pcm, tps, map sensor and drac. There is nothing abnormal in the way it drives. I will have to dig out my data logging stuff. It has run so well in the last long time my data logging is in the back of the shop storeage. Just wondered if anyone had run accross something like that. Also if you have thoughts.