Originally Posted by B350
1. Overheating. I had to abort crawling (1st gear walking speed) a steep, rocky trail in BC when the tranny got hot enough to set off a code with the blinking overdrive button light.
2. Lack of torque. Just the other day I was going up a steep, snowed in trail at about 8500ft elevation and got to a point where the tires were stuck in the snow and the olí 7.3 belched smoke but couldnít turn the tires anymore. Shoveling ensued and with just the slightest amount of movement I was able to get going again.
Unfortunately your symptoms, combined with having a Powerstroke and 4.10 gears, don't bode well.
Crawling at slow speed certainly can make things warm, but even dragging my trailer up steep draws at least 35%, sometimes wheels off the dirt, I've never gotten mine that hot.
And more importantly, I can't imaging situation where I'd stall out. I stuck the right side of my trailer in a muddy tree well this weekend, up to the axles, and had zero issue spinning my tires trying to yank my trailer's 11,000 pounds out of that hole.
I agree that a crawling would help, but I don't think you should have those issues to start with.
That said.... overheated fluid foams and loses viscosity, which can cause symptom 2.
#1 thing I'd check first is that your cooler is actually getting oil flow. Sometimes the 4R100 end up with a stuck pressure relieve valve, which bypasses the cooler loop (which are in series, so both cooler in reality). Aside from rust and old age, they can also properly bypass if the cooler is plugged with debris. But if there's debris in there, your tranny probably doesn't have much life left anyways.
Now, if you can verify oil flow (stick the oil cooler outlet in a bucket and start the van, it should flow a quart per 15 seconds minimum at idle when warm), you might just need a larger oil-to-air cooler. But once you'e gotten your fluid hot enough to stall out or flash the O/D light, you should change it anyways...
That all said... One workaround for a lack of off-the-shelf under-drives, is to go ahead with the Gear Vendors Overdrive, combined with much lower gears. You'll get lower overall ratio needed for off-road driving, but still retain a reasonable top final-driving ratio for highway cruising, AND gain much needed "in-between" ratios. Only real downside is $$$. You don't even have to swap the fuel tank for this. But you do have to drop the tranny to swap the tail shaft.