SURGING PROBLEM

Thanks to all of you who have sent suggestions and ideas of things that might help with finding a solution to my problem. Some of you have had additional questions which I will try to address. I have 80,000 miles on my RV. I have been working on this problem since September, 2019. I find that after the engine is up to normal running temperature and drive 20-25 miles, the surging starts. However, there have been instances where I have gone 40 to 200 miles and some distances in between before I have experienced the surging which I will define more in depth later on. The miles driven before the surging occurs have not been at a specific number of miles. The RV has a 8.1L Workhorse/Chevrolet engine that operates on a Throttle body Assembly with a wire not a cable. To date I have changed the fuel filters, plugs and wires, the transmission has been totally rebuilt with new torque converter, pump, bands and sensors. Additionally, I have changed the TCM Module and had it flashed. What I mean by surging is the tachometer will start surging from 2,000 up to 2,500 rpms and then back to 2,000 rpms. The engine appears to go up in speed as if it is trying to change gears but this does not happen. When the engine appears to be trying to go up in speed the speedometer is not reflecting ANY change in mph. The indication of any change in the engine speed is an audible sound only with no indication of a speed increase on the speedometer. I have made a video of the tachometer and speedometer while running that clearly shows the tachometer surging to 2,500 rpms with the speedometer staying right on the same speed whether 60 or 65 mph. The video picks up the sounds of the engine trying to shift. The amount of time that the surging takes place varies. When it does stop everything goes back to normal operation. It appears that if the transmission is in 6th gear it stays there and does not shift to 5th gear even though it sounds like it is trying to do so. The same thing happens if the transmission is in 5th gear. It stays there. I am in the process of changing out the HO2 sensors and the Manifold Absolute Pressure (MAP) sensor. I hope this clarifies some of your questions.