Have you considered another pad? Toyota does a lot of things well, one of them is matching pads to stock 275-70 tires. Their criteria is something like, a good all-around pad with no bad habits for normal USA (soccer mom) driving. I wasn’t impressed with them and switch to EBC’s with better results. For your use, offroad and limited street miles, pad life isn’t as important as good strong initial bite. A lot of performance pads are geared towards sports cars, they have great friction and produce great stopping numbers, but are hard and must be hot to do it. We are looking for a softer pad that works well cold. The basic EBC Green Stuff pads are Kevlar, they make little dust and it rinses off, the only bad habit I have see is they groan sometimes offroad, but they have great bite and are very easy on rotors.
http://www.ebcbrakes.com/greenstuffinfo.html
Yep, go out to your favorite wide open, relatively level dirt road, pull the ABS fuse, have the CDL unlocked and have a helper watch. Make several passes and get a feel for how much pedal pressure it takes to lock the fronts. Then try to lock the rears, they should lock with just slightly more pressure and slightly after the fronts. Then you may want to confirm it on pavement, the dynamics are different.
The LSPV’s job is to sense the load in the rear and adjust the rear brakes accordingly. With a big load in the back it puts more pressure to the rears, when there is no load and a big braking event, the rear pitches up and the valve cuts of the pressure to the rears to prevent them from prematurely locking and the truck spinning.
When the truck is lifted the valve sees it as a light load and pitched up, cutting off the rears. With your lift and weight, my guess is that you will need the frame adjustment all of the way down and may need to make a simple bracket to rise the axle mount end to get the rears to come on strong.
The adjustment is very simple to do, only need to loosen 3 10mm nuts. I would tune it on both trucks, you will be pleasantly surprised at the brakeing improvement when it's properly adjusted.