Speedometer Drops to Zero

This has stumped both the local Bobcat & Polaris dealers. It doesn't help that Central Oregon has become a desert for servicing the Brutus since Polaris gave the service contract to a different Polaris dealer and they have chosen to service Brutus units only at their main location 150 mi away. After startup, push on the accelerator, even very gently, the Brutus accelerates but speedometer stays at zero or blips up briefly and goes back to zero. Speed is slower than is should be for the given "gear" and RPM's are higher. This happens regardless of gear or drive selection. Wheel speed sensor has been replaced with no effect. It happens fairly frequently but much more frequently than when I first purchased it 5 yrs ago. It is reliably solved by slightly easing off and then re-applying pressure on the accelerator but sometimes this needs to be repeated 1-2 times. This still happens when warmed up but less frequently. As it reverts to normal with the accelerator treatment, it has the feeling of some hydraulic valve finally opening allowing the speedometer to function and RPM/speed to normalize. The Polaris dealer asked if the check engine light came on. It does not. This is the only issue with it. Any thoughts? Thank you.