3:42 rears

I have a 2013 Pete 388, 70" standup sleeper with 268" WB . It has 550 hp, 1850 torque , 18 speed Eaton with 3.42 rears . Truck is dbl framed back half of truck , holland fw35 5th wheel, air trac suspension , 46k drives on 11R24.5 rubber . It has a Muncie dual line wet kit, with a rgn jack plate on rear of frame for detaching hydraulic neck . Do yall think the 3.42 rears will pull a 6 or 8 % grade . Or should I swap for 3.90 rears .
I would like to pull the load not creep down the road

 

So , should I change my gears to 3.90 gears

 

Around 1500

 

My other truck is a 2013 Volvo 630 mid roof sleeper . 500 hp , 1750 torque 3.55 rears and 13 speed Eaton with Volvo d13 . I've pulled cat gens and gross 107k and it pulls fairly well, so I would think isx 15 550 hp 1850 torque would pull better but pete has the 3.42 gears .I'm not worried in losing mph cause the pete will do 90 and 65 mph is fast enough with oversized loads but going up grades would like to be able to maintain at least 40mph . Most of our loads are heavy equipment like 326 excavator, 336 excavator but would need a jo jeep and a fee link belts that are around 105k weight just the machine. So I would like to see what I would need to change to not drop 3 gears or more.