I would say that's not true.
first, your transmission won't shift to OD until about 45, so below this, it won't make a single difference. (might be a bit lower if you have 4.10's)
above that, your transmission is set up to downshift before it gets too low in the RPM range, so it should not make a difference there either.
if you're towing something more than, oh, say 5Klbs or so, I would shut it off because i've heard the OD clutches aren't really made for towing. don't know how true this is though...
96 Powerstroke: 6637, downpipe to dump exhaust, 140v IDM and a shift kit.
84 Honda Sabre V65 1100: pipes, jet kit and new tires. Faster than I think I'll ever need.
I would also say false, I have had one for over 20 years I'm the original owner and my truck was the first month production E4OD and I have never drove it with the od off. The only thing ever done to my trans has been fluid changes about every 30,000 miles. It has a 4.10 axle also
2015 Challenger HellCat Redline Red 8sp
1997 F350 4X4 CCLB PSD
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1999.5 Jetta TDI 11mm pump S7 PP764's 3bar MAP
1986 F350 CC Dually 6.9 ATS turbo lowered
1984 Mark VII 2.4 BMW Turbo Diesel
1970 Roadrunner 383 4sp
1970 Cuda 426 4sp Dana 60
I have heard the e40d and 4r100 in the superdutys are built to tow in overdrive. The only reason you should take it out, is if ur towing at a speed that tranny is shifting in and out of overdrive a lot. That will excessive heat and wear. Thats what i have heard and read before.
2000 F-250 ext cab 4x4 6 spd. Glowshift gauges(egt, boost, and fuel pressure), PHP tuned, DIY intake. MBRP 5 inch straight exhaust with 6 inch tip