swaping the gears im not sure..
but a trailer that size you should be using a truck with Dully ..
sorry to say ..
tires on the trailer get a TPS system .. watch the heat .. i have china bomb's on my trailer But,
i do not push my truck or my self ....
any Any truck can all most pull any thing you put be hind it BUT BUT!!
when it come to Grade % up hill down hill thats when your truck is going to be push to it limits .with no jake brake relying only on your skil's..
my truck is a 2000 quad cab 8' bed 4X4 dana 60 F dana 80 R 4.10 gears Dully 5.9 cummins. Rancho XL9000, over load leaf. new trans with a ton of up grades..
but my truck is still limited ..it's a auto not a standard
just my take ...
check out BIG TRUCK BIG RIG on YouTube tums of info and how to ...
good luck