[twindman]

My problem with the speed is this. I thought my Silverado wasn't shifting into 6th gear. Experimented and found by research the it doesn't shift until around 68mph. I had my top speed at 62 or there abouts. Someone else had noticed this and said the mpg seemed to be almost the same at 62 or 68. You lose by speeding, but then gain by shifting into 6th. I haven't tried 68 for extended time yet, but may try this summer to test it.