Need help regarding gear ratio

Hi everyone, my name is ravinder I’m from British Columbia,canada. I recently bought a peterbilt 579 with x15 500hp 1850 torque, 3.25 gear ratio,235 wheel base, meritor 2014x4dcrnn742 differentials,12 speed eaton endurant hd amt tranny, i used to do jet fuel for trimac as a company driver nd really liked it but then I decided to grow and wanted to be an owner op, as I’m new in heavy haul(tanker) industry I didn’t had that much knowledge about choosing the specs,so I got a good deal with my truck nd bought it, but unfortunately trimac said no to me cus it’s not heavy spec, now I have another opportunity from some company to do a local run for fuel superb’s but the problem is there’s 3 steep hills to climb on my way back from the refinery..nd I’m really confused if my truck with above mentioned specs can haul it? Or do i need to get the gear ratio and diffs changed?? If yes can someone please let me know what can be possible with my current setup? Hoping to hear back soon from you guys, and sorry if this is a dumb question any little help would be appreciated.

 

My truck is governed at 105 kmph or 65mph and it goes upto 1350 rpms, you think it’s possible to climb a 5 or 6 percent long steep hill with a loaded full gross super b?

 

I am sorry sir, i have less knowledge regarding the specs… i am bit scared, i called the local peterbilt guys nd they said if my gear ratio is 3.25 im gonna be unable to climb the mountains, nd end up breaking my tranny cus its 12 speed automatic ,they said the rpms are gonna keep dropping and not gonna give enough power

 

Yes 1350 in high gear…if I cruise at 65 the rpms sits at 1350