RV 4 2,
Per Power Gear literature, I've used Castrol ATF Dextron III in my Power Gear reservoir when low. You might call Power Gear to verify with your 2008 unit.
2005 National RV, 36' Dolphin 5355, W22 - Front & Rear trac bars, IPD rear anti-sway bar, Koni FSD Shocks, UltraPower programming.
2000 Jeep Wrangler, Brake Buddy