Well tried a Airtronics Tx and Rx today, same thing. While testing tho, at one point, the truck didn't move when giving it throttle....just a big "whirr" like if your pinion lost its mesh.

Put it on a stand and took off the cover, nope, mesh is good. Checked slipper clutch setting, nope, thats good. Turned it on and gave it throttle, spur turned but not the tires. Tried a quick burst of throttle and all of a sudden it "clunked" into gear.
Transmission.....great.

Called Horizon to get some input and I was lucky enough to talk to a rep that actually owns a converted LST-XXL. After telling him of the issues, he knew right away what was going on.

To cut it short, what I need is the "forward only" transmission conversion kit and that should fix all my issues. He explained it to me pretty good but I won't go into it all the details. Wish I knew about this sooner.