2006 Silverado 5.3Lv8 with 55k miles on it. I pulled out of the parking lot today and came to a complete stop at the stop sign, put my foot on the gas to go and nothing happened - almost like the truck had slipped into Neutral. I dropped the truck into 1st gear and was able to move. At about 1500rpm I shifted up into 2nd and again into 3rd at close to 1800rpm. Reverse is still working like a champ. While I was checking a few other things out, I was able to shift out of park with my foot off of the brake pedal. Crawled under the truck and in Drive the drive shaft wasnt turning, but it wasin '1' and '2', but not 3. When its in Drive and a little gas, the tach jumps up but the truck doesnt move. I did check the speedodometer, thinking maybe it was a speed sensor keeping it from shifting into drive, but the speedomoter is working. Fingers crossed that its not going to be a transmission rebuild...any thoughts? Thanks guys!!!