You're right, Dave: NOW is the time!
The PowerTrax is basically a Detroit Locker clone. Check it out here to see how much better than any limited slip it is. Click the middle video to see a big Cummins Dodge HD with
two limited slips get it's butt
kicked by an old 2wd Ford with a single PowerTrax:
POWERTRAX BY RICHMOND VIDEO DEMOS
In the case of the Dana 80, the drop-in design (if you have an open factory carrier) is just like the drop-in design of the Detroit Locker in the GM 10 1/2 inch Corp 14 bolt.
You may have heard varying stories about drop-in or "lunchbox" lockers that utilize the factory carrier. The bad reputation some of them, like Lock Rite, designed for smaller car differentials, get is because the factory carrier is often too weak to handle full power going to both tires, and the pavement, at once.
That is NOT a problem with the massive and beefy Dana 80 or the Corp 14 bolt. They can handle it. Guys who take a factory 7 1/2 inch rearend, drop in a locker, put wide tires on, then hook it all up to a nitrous motor putting out 500+ hp tend to blame the locker when it all grenades when it was really the factory carrier, axle shafts, etc. that couldn't take it.
You talk about carrying some very heavy loads frequently. One thing to keep in mind is how much traction that puts to the ground. With a locker, or possibly even a very tight limited slip, you will be putting some serious stress on all of your axle components. I believe they should be up to the task, but I have read where others found a locker
too effective when pulling very heavy and turning tight. At any rate, if there is a weak component, that is a fast way to find it.
You may indeed be better off with a selectable locker if you can afford the extra $$.
If I had my choice of selectables, I would opt for the Ox locker in a rear axle. No air lines; just a very positive engage/disengage aircraft stainless steel cable actuator. They are supposed to be brutally strong, too. the cost is about the same as an ARB last I looked.
Living in Idaho, your truck is subject to extreme temps throughout the year. Not only will Amsoil synthetic protect MUCH better under higher axle temps, no conventional oil even comes close to resisting thermal breakdown as well, it will also protect and flow much better when the mercury drops to the brutally cold end of the tube. All year round, you will see less friction, lower differential temps, and a slight increase in mpg running synthetics. In a long-term personal vehicle like a Cummins Dodge, Amsoil products in all your components will save you money and extend their life. It is cost-effective.
I was always very pleased with the protection my vehicles, from my John Deere lawnmower, boat motors, 97k mile '83 motorhome, to the Cummins, to our
extremely abused motocross race bikes, got from Mobil 1. But as you already discovered, Mobil 1 has a problem with causing seal leaks. We switched everything to Amsoil and the leaks went away and the protection is even better. If it doesn't say Amsoil on it, I don't buy it.
My son, when he was much younger and got his first YZ85 race bike, accidently used the gas can marked "Yamaha" for my 4-stroke race bike. He ran that 2-stroke HARD for over an hour on straight gasoline!! When I got home from work and confirmed what had happened (I only knew because he told me how long and hard he had practiced on his new bike, and I knew we did not have any 2-stroke gas for it and I cringed, knowing the answer, as I asked him to show me what gas he used). I know of many other instances where straight gas was accidently put into these 2-stroke race bikes and the results were always catastrophic and almost immediate. Like putting gasoline in your Cummins.
I dumped out the tank, refilled it with our synthetic 2-stroke mix, turned him loose, and waited to see what would happen. It never missed a beat. It did not even need a ring-job! Unbelievable!! I also changed the marking on that can since we now owned two very different Yamahas...
He went on to race that bike to 10 different track and season Championships over the next 4 years and I NEVER have touched the bottom end!!
It is still running strong to this day. Wow!! That
little bit of oil mixed in the gas at a 40:1 ratio is the ONLY thing that lubricates the crank and rod bearings and cylinder! The film left by synthetics on metal parts is THAT strong and slippery! In fact, whenever we do routine top-ends on our race-bikes, I MUST use el-cheapo conventional 2-stroke oil for the first tankful or the rings will NOT seat due to the ultra-slippery coating left on the cylinder wall.
How much better proof of the superiority and protection of synthetics could I ask for? Those motors are subjected to 10k to 13k rpm's constantly with radiators plugged with mud, over revs, slam shifting, etc.
None of our 13 different race bikes in over 10 years of racing has
ever shucked a crank, rod, or top end. And all but two of those bikes were bought used! So don't ever think it is too late to switch.
It does cost me $120 to change oil and filter on my Cummins with Amsoil 3000 series oil and the matching Amsoil filter, but I only change it once a year now. It has been a year of hard use and snowplowing and it is due for a change now, and it is showing only 1/2 quart low on the dipstick with NONE having ever been added since the last change. I can definitely live with that low oil leakage/consumption! If I were to invest wisely in their oil bypass filter system, I would not even need to change it that often. Just the filter. Do a search here on TDR and see how many guys are running Amsoil and bypass systems.
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