I've used this tune and wondered how to make it quicker, so I dived into the tuning menu to have a look.
Note: This is on RS tires.
Change 1: Lowered Initial to 5 for front and rear, and set power limiter to 89.2% (Keeps it at 550pp). Lap time: 6:56.187
Change 2: Lowered Accel sensitivity to 15 for front and rear diff. Lap time: 6:51.983
Lowering the HP, changing the tires and adjusting the diff has me two seconds off your best time in the RAM.