Chevy Silverado 1500 Intermittent shift issues

I have a 2007 Z71 5.3 that every week or so upon acceleration from a complete stop seems to miss gears after 2nd. The RPMs raise, but the truck feels as thought it is neutral. I can manually shift into 3rd and the problem persists. I can shift to 2nd and the truck goes back into gear, but will not engage in 3rd or drive. I have to stop and place the truck in park to correct the problem. I took the truck to the dealership and was told the transmission fluid was a little high and was asked who serviced it last. The service tech checked my records and realized that dealership was the only service department my truck had been to since it was purchased from their lot. I paid $271.00 for diagnostics and a new gasket and was told to call if it occurred again and I would not be charged a diagnostic fee. The problem occurred again this morning, I phoned the sevice tech, he consulted with the transmission tech and told me it sounds like an "overrun clutch" with an estimated repair price of 1500.00, but they couldnt be sure until they were inside and it could be more. My truck is not throwing a code when this happens. Any advice would be appreciated.