Transmission problem

[02XLT150]

Once in while when accelerating(going through all the gears) on the highway, the transmission will skip fourth gear and go right into overdrive. I can turn off overdrive and the truck will stay in third gear, but I can feel that overdrive still kicks in. Is this a computer issue, or is this a sign of transmission failure? I had the fluid changed about a year ago. I am also using custom tunes on the Gryphon. Any advice would be appreciated.