Increase the idle setting!
I had to do this also. Some people are obsessed with slow idle speeds on engines and diesels DONT LIKE IT!
Raise the bed (and set the safety-strut) and have someone press the “accelerator” pedal and you’ll notice that the idle control lever (right-side, front of engine) has a hex-head bolt that is safety-wired. That is your idle adjustment.
INcrease the idle speed until it smooths out.
This will not affect your RTV movement from standstill. The “accelerator” pedal actually controls the VHT (transmission) speed, and the engine will accelerate in symphony with increased vehicle speed.
I had to do the same thing and the little RTV has performed flawlessly since.