I know you want it fixed, but if that doesn't happen (right away), a decent cheap throttle lock can give you needed hand relief doing distance (with some occasional adjustments for elevations).
The main trick with throttle locks is adjusting them for tightness. You always want to be able to overcome it easily with your hand while locked on, but too lose and they back off over time and bumps.
I'd seriously look for a used Brake-Away.
Ran a number of throttle locks over the years. This version is head and shoulders above the rest.