Freightliner glider questions

I'm looking at modifying a truck for hauling side dump trailers, am I wasting my time with putting heavier axles under a truck and making the required upgrades to the suspension to make the increased GVWR when I could get a glider kit that's done up how I'd like it done and have some additional benefits like a heavier duty frame, wet line kit installed, adjustable fifth wheel with air release for when the lever isn't wanting to cooperate, etc. Another thing I'm wondering about is if some sort of assist is needed on the passenger side with an axle rated for 16,000 pounds or if that's needed on 18,000 and 20,000 pound axles. Would it be worth looking at a 15 speed over a 10 speed like what's in the truck I'm eyeing? Or should I go all the way up to an 18 speed? I'm leaning towards sticking with Detroit as I have most of my experience with the DD15 and so I figure I'd have even less issues with the Series 60 as I'm not even familiar enough with Cummins to say I dislike them and I've never dealt with Cat. Sorry about rambling.

 

Okay well if for no other reason than input torque rating on warranty I'd go with an 18 speed because 2,250 lb ft of torque is a lot of room to work with on the engine side of modifications

 

Just talking axle ratings the Freightliner my current and soon to be former employer (by choice, better home time and better pay) is built stoughter than I thought at first, the steer is 13,300 and the drives are 40,000, whereas the Columbia I'm eyeing is listed as 40,000 on the drives, 12,000 on the steer, and unknown for the pusher axle, although considering it's running what look to me like 11r22.5s it's between 12,000 and 16,000. Also with Utah the steer axle weight limit is whatever your axle or tires are listed for, can't remember which, so it would actually help with capacity.

 

Plus seeing what the 15 is rated for doesn't leave a lot of room for more power should it be needed, I'm thinking right now I'd see how it feels at 515 and if I do go higher I'd probably only go to 600~650 because of cooling concerns because there's an unnecessary amount of mountains in my part of Utah and so going to 700+ might get into risky coolant temps in the summer, plus questions of longevity

 

Although this brings up the other question playing around in my head, would I be better off getting a glider and ordering it with this already done? It'd also open up the door to a beefier frame, along the lines of 1/2" thick rails. I don't imagine I'd ever need that much strength but it's better to have it and not need it as opposed being 3/8", getting stuck in the mud somewhere and getting the front end torn off because someone thought it'd be smart to try and pull it out instead of calling a rotator, assuming one could be called for