Vibration in Gas Pedal/Overdrive

[xFatcatx]

99 Sport, 78000miles, 4wd, 4.0L SOHC, 5R55E. I recently started feeling a vibration in the gas pedal around 45-50mph. I didnt pay much attention to it but it started getting more noticeable and happening more often over the past week. After messing around with it I realized it is only when driving with Overdrive on all of the time. At 45mph, with overdrive on and the vibration happening, I can turn off the overdrive and the vibration will go away. For the past few days I have been driving around town with OD off and only turning it on at about 50mph when hopping on the expressway and freeway and have not had any more vibrations in the gas pedal. I recently (4 months ago or so) fixed my 2-3 flare with a remanned VB. It almost feels (with OD on all the time) like a bogging when trying to shift into overdrive. Like driving a manuel tranny and needing to downshift. Any help appreciated. Maybe everyone could chime in and see if you guys drive with OD on all the time, or turn it on and off when needed. I have been told that it does not affect the truck to drive with OD on all the time but I am beginning to be skeptical about that. Thanks