The basic mechanical design of the E4OD is sound. Some of the internal components of the earlier variants were weak, but not as weak as some would have you believe. One of the biggest flaws to this day, is the mechanical complexity. If you watch a teardown video of the E4OD and compare it to the modern 6 and 10 speed RWD autos, the E4 seems more complicated. The electronics on the newer ones take up the difference because software and ECUs were not up to the task of friction to friction shifting in the late 80s. Although, because there are no friction to friction shifts in the E4OD, it's also a bit more fail-safe when electronics go wrong.
And yes, I use the OD lockout. Not to save spare the transmission, but to prevent hunting and lugging the engine under some conditions. As I've said many times before, the Overdrive planetary of the E4OD is physically larger than the main forward planetary. All power that enters the transmission first comes in through the Overdrive section, so locking out overdrive will not spare any torque from going through there. Lower RPM can lug the engine and reduce flow to the trans cooler, but if the converter is locked, there isn't much heat generated anyway, even under heavy load. Bottom line, just use whatever gear makes sense.
I can climb a 5% grade at 55 MPH in overdrive with 850 EGTs, or hit the lockout and climb the same hill in 3rd gear with 650 EGTs. I do run 3/8" cooler lines and an aftermarket cooler. So far, this seems to actually overcool the transmission under most conditions.
My only gripe right now, is the shift logic use to manage the converter lockup. Apparently it's a limitation of the older aftermarket controller I'm using. I'll upgrade some day to the newer US Shift unit that others on here are using.