Which setup ?

A tractor/trailer will not do well in mud etc. especially one set up for on road use.
I logged and sawmilled for 30 years before trucking. I hauled on bob trucks without trailers for the most part. Your truck with a pup trailer would probably be fine since it’s set up for logging but if you take a regular road tractor and use it to pull a log trailer you better be ready to pull it out with a skidded quite often.
I have seen road tractors get stuck on a little uneven ground and also on a small patch of ice or snow.

 

This will depend on where you are logging and how the roads are built. Neither one is going to get around empty in mud or snow, unless you have the pup loaded on to the tractor for traction, period, especially if you have some steep ground in there.
Where I log no one can use a regular trailer, the turns are too sharp, and there is not enough driver weight on an empty trailer to get you back anywhere close to where the logging is going on, except for the driest days of summer. You load the pup on the empty truck to get in empty and the truck turns into a mountain goat, throw some cahins and it takes some serious snow to stop it, now coming out loaded a steerable log trailer is much better, I will not pull my pup in bad snow and we can't get in with anything when it is muddy here, so do not even try, usually.
I have hauled some loads when it was muddy for the skidder had to pull me the first few miles, it is not generally worth it.

 

If you mud is just greasy you may get by, if it is soft even chains will not help
I am not picturing what kind of truck and pup you are talking about with a fifth wheel mounted knuckle boom and still being able to use your fifth wheel to pull an equipment trailer. I haul my loggers smaller equipment, but on a 3 axle pintle hitch tilt trailer.

 

How heavy are you allowed to be?
Gross weight.

 

Sit on your hands a little while longer i think. The timber dictates the equipment. You dont haul whole tree pulp on a straight truck + pup and you cant usually get a tractor and pulp trailer into a small private stave cut.

I am concluding that since you havent mentioned the timber you probably havent got the jobs lined up, and youll need that above all things to keep the checks coming in. Logging is a perpetual struggle and jumping into equipment without a pretty good idea of where you can show up to work it is risky.

A straight truck with 5th wheel and removable back bolster can move the KB from job to job. But you have to be on site when the loader is loading for a straight truck and still get to the mill during dock hours. With trailers you can park one at the KB in the middle of the night and go haul the full one during the day while the other gets loaded. But then youre beholden to the pulp market and usually one big mill.

A rear mounted self loader triaxle straight truck probably has the least efficiency in terms of tonnage, but the most independance to jump from job to job at any hour, in hardwood anyway. Or straight truck with pintle pup and log loader on front of that. Would never work for hardwood pulp whole tree.

So to talk trucks we need to be talkin timber and markets first. Who do you know and whatre they offering? Where you haulin to and whats it pay?

[And what experience have you got?]

 

Another option is to hedge your logging bet.

Buy a good dump truck. Walking beams, 8LL or 15 speed, full lockers. Take the box and hoist off and park it. Build your 4 pole log bed with a stinger pintle and run it. Buy or build a pup as you can. The dump pto could be used to power a self load trailer which would let you go out and cover little jobs where a contractor has no knuckleboom, or maybe you get a skidder/dozer of your own some day.

If timber goes in the toilet put the box back on and haul shotrock, gravels, lime, coal, firewood, whatever.

 

The self loaders I have been around all used a three stage pump, a regular pump like on a dump truck would not work, or if it did, not very good I wouldn't think.