BCI, you sound very knowledgeable, but is this really true?
"Worse your insurance won't be valid if anything happens and you're overloaded."
Good catch - I'm being presumptuous there. Every territory is going to be different, so I shouldn't say it's an absolute. I would say that my experience with insurance companies is they're happy to cash your premium checks, and they are loathe to pay out coverages.
Insurance companies are always looking for reasons to deny coverage and keep their profits. Remember that a truck is designed for it's rated capacities with appropriate front and rear springs, tire ratings, and brake size for those loads. Go over those loads and you're on your own. I wouldn't want to find out the hard way what happens if you overload the design parameters and you end up being 'at fault' in a serious collision. A minor rear ender probably nobody cares. You kill someone, and you're open to be liable for putting something on the road that isn't safe to stop in time or handle appropriately.
I just did a quick search and found the following in BC and Ontario message boards. Granted some are related to towing, and some are for payload, but it all shakes out the same for capacities of the tires, axles, brakes, etc;
PASTE 1;
if you are overweight and get into a wreck, and the accident investigation determines you were overweight, your insurance company can (and probably will) default your policy, which means you're not insured. If you just hit the ditch, you might only have to replace your vehicle. If you are involved with another vehicle and injure (or god forbid - kill..) someone, you can probably expect to lose a lot more.
Its not worth it. Find a suitable vehicle.
PASTE 2;
There is lots of chatter like this on RV forums (where tow limits are regularly tested)
Exceed the tow rating, tire or axle ratings, gvwr or gcwr and you're leaving yourself open to be screwed.
Likewise the mods, sure they make it safer but don't change any of the numbers above so you're still screwed. They will also get you for undeclared mods.
Stay within your official rated limits (and prove it with a slip from a certified scale)
Cheers
PASTE 3;
In my experience an insurance company will look for any out they have available to delay or decline payment. Towing a load higher than the capacity of the truck is a huge opportunity for them to do this. As for the upgrades, that may give them the opportunity to claim you modified the vehicle and did not inform them. This would also give them something to take issue with.