2nd Gen Durability at Max GVWR

I tow a small fiberglass trailer that weighs around 3300 lb fully loaded. I also carry a significant amount of gear in the bed of my 2010 SWB 4WD CC LE with a Leer fiberglass canopy. I replaced a 2001 Ford Ranger 4WD SC last fall with the Frontier because of an almost catastrophic bearing/axle failure earlier in the year in the middle of nowhere NV at 115K miles. The good part of the story was the mechanic I limped into in Delta UT fixed me up with 2 new axles, bearings and brakes for ... get this... only $700 total and my wife and I were back on the road within 24 hours on our vacation. Long story short, the Ranger axle is a semi-floating bearing design with no inner race. The bearings run on an induction hardened surface of the axle.

So I have two questions:

1) It appears from the factory service manual that the Frontier C200k rear axle has a full floating bearing with an inner race. (Interestingly, the M226 axle appears to be a semi-floating design.) So here's the question for the rear axle specialists on this forum: how durable is the C200k axle with heavy loads? I'd always figured the tires were the limiting factor on GAWR until the bearing experience with my Ranger. Any recommendations for axle lube? I'm thinking about replacing the factory 75-90W with Amsoil 75-90W for better oil film strength.

2) The payload on a fully optioned LE CC isn't very much. Especially with the addition of a Leer fiberglass canopy. Per the placard, GVWR is 5815 - 198 = 5613lb. GWR front axle = 3296lb. GWR rear axle = 3331lb. I have added Firestone Ride-Rite air bags and use a weight distributing hitch with my trailer that has trailer brakes. I don't do any technical off-roading with the 4WD. I plan to weight the truck including each axle separately with and without the trailer hitched to see exactly how much payload (persons & gear) I actually can carry at the GVWR. I still think the tires are the weak link but wonder about the durability of 2nd Gen Frontiers and especially the rear axle when loaded at GVWR (or maybe 5% over). What is your experience with towing and hauling at max GVWR?

Thanks in advance for sharing your experience and advice.