Your post is a bit confusing (to me anyway :/ ), you say that you can't slow the truck down without a "jump"? Describe this jump. As far as the auto braking, would you rather replace brake shoes or a trans? The auto brake works by engaging the opposite direction clutch pack of the selected direction the trans is presently in (if going forward, engages the Rev clutch pack etc). Anyone with a mechanical knowledge of trans realizes that this severly overheats & wears the clutch packs. I always advise my customers to turn this function off as a brake job is MUCH less expensive than a trans job.

If the brakes are working correctly then slowing the machine should be like any other forklift.

If you still want this function, and the trans is working ok with no engagement issues in f/r, then I don't understand why they say you need a trans, the computer dictates when & how the trans engages. I would ask for a detailed explanation of why a new trans is needed- sounds suspicious to me