Heavy Spec Tractor

If I'm reading you rt it shouldn't be a problem if you don't horse it to much,I used a not so heavy spec trk for year's.it worked well for me.

 

IMO, the main thing would be what trans you have. 13 or 18 speed would be best, a 10 speed not so good.

There are plenty of single framed, 38K rear trucks pulling 55 ton trailers. Just don't dog it and it will be fine.

 

You should be fine with that setup, I've seen people do a lot more with a lot less.

With the 18 speed I wouldn't even worry about changing the rear ratio.

 

I have not personally ran a light spec truck on 8 axles, but know a couple of guys that have. They were actually normal road truck 379 Petes with an added pusher axle, 12k steer and 40k rears. From what I learned from them between the two that you may be ok with 3.73 ratio depending how much you run in the mountains and what your tire size is. A low pro 22.5" (295/75R/22.5) tire with 3.73 ratio is about the same gearing as running 11R/24.5" tires with 4.10 ratio. I would try running what you have first to see how it performs.
If running mountains a bit make sure your rear end gauges work. One of the guys I know said his rear ends would overheat whether he was going uphill or down. Why downhill is because of running jakes (I guess). He ended up non-synthetic gear oil because it was cheaper and changed it quite frequently from all the heating cycles.

Congrats on the new Trail King. They build an awesome trailer.

 

I used 373 for years up to 220000 the unless you are going higher than that . If you're going 250 300 thou than put in a 2 speed rear