98' 6x4 throttle "twitchy" "jerky" at medium speeds

Im new to the forum. I've had a Trail Gator for years. I bought this 6x4 Trail Gator new in October'98. It's a hardworking farming,hunting, riding Gator.
This throttle issue has been long term. I've done all the maintainence my self.
She's never been to the shop as I've had no major issues, except this chronic power application issue.

Start, warmup idle are normal. Driving off is fine. When I get to "mid level" accelerating the throttle/accelerator peddle produces a twitchy,jerky input to the engine. I have run with the cargo box UP and observed what I think is the governor arm flipping in and out as this twitch jerky behavior occurs,despite the spring attached . The throttle cable moves smoothly, the engine makes full Power . I cannot operate easily at slower medium range speed without this jumpy Jerky engine behavior. Going over rough terrain slowly makes this worse.

Though she's 14, she's well maintained and works hard. I Do regular oil changes, she's had a new belt and chains in last year or so. I replaced the cargo lift relays yesterday, cleaned undercarriage and blew out all debris from nooks and crannies.

Is there a "Carb Kit" or "Governor/Carb Kit" or other adjustment to smooth out the mid range acceleration issue?

Thanks y'all