The problem that I am having is that when I get up into overdrive, and I am maintaining steady throtle with no load (level ground), my 98 Chev 6.5 L diesel 4L80 tranny auto, is acting as if I am not in gear. It feels like I am driving a standard with the clutch in and my foot on the accelerator. The problem only seems to happen when I am in OD, but I took it into a tranny shop, and the guy has never seen a similar problem to this in his 30 years.

He seemed to think that this problem will only happen once the transmission locks in, which happens on my truck at 76 KMH (47.5 MPH). He said that the problem will only occur when I am into the throtle less than 10%. He thinks it will happen in third also, but I couldn't make the problem happen in third because it was difficult to get the engine to lock in and mantain a steady throttle at less than 10%. He advised that I change the APP, but he wasn't sure that would fix it. Also, he was using snap on diagnostic equiptment, and there were no codes tripped. Also, once I am in to the throttle more than 10% it seems to fix it, but at the same time, it is usually once I raise the RPM by 300-400. I don't know which of the two would give you a better idea.

Have you ever seen anything like this before?

Thanks very much,