'04 Hemi QC auto w/3.92 rear end and ~58k mi.

About to make my first longish interstate haul (6 hrs round trip) with my 6,500 lb boat/trailer. I normally just pull it 4 miles down the road to the launch and back. I've always used the tow/haul button when pulling it in town.

Should I do the same when cruising at 65-70 on the highway? Or can I get up to cruising speed and turn off Tow/Haul to save some gas and let the engine turn lower RPM then just press the button again when climbing hills? I'll be in relatively flat land the whole time. I don't care about gaining 1 MPG if it's detrimental to the life of my transmission though.

It's up to date on all maintenance (Rear end and ATF have been changed in the last 5-6,000 miles) accept spark plugs which I plan on doing this weekend (Technically it's up to date through 60k on those though). BTW the manual states to change the spark plug wires @ 60k. Is this really necessary? I don't think I've ever changed those on another vehicle before 100+k.

 

I suspect tow/haul application may depend on terrain. Flat ground may not need it so much. I'd wait on the plugs 'til you get back.

I didn't change my plug wires 'til 111K. It seemed to improve the mileage, but by too much to be reasonable, so it must be a fluke.