"at 7000lb trailer tongue weight is around 1050lb"
Whoever set up your WDH and trailer loading did you no favors. Not that it is excessive as its in range but it is more load on your truck than need be. Even with a box front travel trailer at 65 mph 12.0 percent or 840 pounds put with a replaced steer weight is more than sufficient to stave sway, semi truck bow wave, or strong wind gusts. 10 percent or 700 pounds as Groppelt set his to is often sufficient.
"The 1500 is just not made to be pulling that weight"
That does not match what Ram engineers and or SAE Society of automotive engineers J2807 tow standards say. Both the tongue weight and the gross weight I can attest to with almost 800,000 miles towing TTs with the 1500.
In fact set up optimally with WDH according to CAT scale results the 4th gen 1500 platform (including proper gears & motor) can handle up to 8k well without exceeding axles, receiver, max tow or CVWR with the only exception being the least important with respects to stability & safety GVWR. This is good for OP to know as his 6,700 pound dry trailer will likely turn into 7,700 when camp ready.
Agree with other poster, what is Ram's idea of lifetime. ZF recommended fluid changes for dusty environments or hard applications such a racing or towing. I change mine every 100k with the Valvoline Maxlife full synthetic that meets this transmissions requirements as it's inexpensive in the gallon jugs. If you shop the filterpans online you can get them cheap now also. My first trans went 700k until a simple solenoid failed. Unfortunately it was built into the board and the dealership said $2,200 to fix. Instead I got a used 70k mile unit out of a salvage yard for $1260 plus simple swap labor. Its worked flawlessly for another 100k so far. If this has held up behind a 465 foot pound torque tuned Ecodiesel it should do well behind a 410 torque Hemi. Both trucks use the 3.92.
When I tow the whole day I end up stopping one less time for fuel towing at 65 vs 70 mph. What I gained on the road I lost sitting at the fuel pump. Its not as hard on the truck in general.