You can replace a failed Atwood Levelegs control system with a GAMA Electronics RF340-4PR-ASL controller for around $235, which is much cheaper than OEM replacement or repair. This aftermarket solution provides better reliability and easier troubleshooting than the original Atwood system.
Given your situation with the problematic Atwood Level Legs on your '06 Pace Arrow 38L, you should keep them and sell the parts yourself - they're worth significantly more than what BigFoot would credit you.
When electric leveling jacks click but won't extend, the issue is typically a blown fuse, low battery power, faulty relay, or hydraulic fluid problem. Start by checking the fuse box and battery connections before moving to more complex diagnostics.
Your symptoms point to a leak in the rear air bag system or cross-plumbing between tanks. The gurgling sound and faster rear sag indicate air transferring from front to rear tank through a compromised component.