the TC still locks up in 3rd with the OD off button
here, ill give you a simple test you can play with (if you want)
turn od on approach a hill and gradually apply throttle until it kicks down to 3rd, given the behavior of the 42RLE, itll be 3rd Unlocked , note RPM's when it does this. and press the OD off button(to disable OD).. the rpm's will now drop, by pressing the od button fairly soon after triggering the downshift to 3rd unlocked, you've triggered a decision/check process that the transmission will eventually start to do anyway but its now operating under the new understanding that 4th gear unlocked/locked is no longer available via the TCM. Once the RPMs drop and stabilize you can begin to reapply throttle slowly and the rpms will hesitate to rise (grunt/lug/drone/etc) until you've exceeded the limits of the TC lockup parameters and it again unlocks the TC and the rpms raise. That's the TC lockup/unlock in 3rd. (2nd gear would be about 1,000 RPM higher give or take since the 42RLE's gear ratios are garbage and there should be an additional gear in there)
there's a TC lockup in 2nd as well if you accelerate gradually enough for it to utilize it and not skip to third. to actually prevent TC lockup you have to inturrupt the LR/LU solenoid while still making the TCM think it's still connected otherwise the transmission will go into limp mode. and the 42 generates an unhealthy amount of heat unlocked which is actually the purpose of the OD off button, the 42's OD is 0.69 which for reference the 45RFE has a 0.75 OD. In otherwords for other than gas meisers on flat roads sipping petrol on 70mph cruise control on eco tires, it's too tall for our application. which means it's going to want to excessively unlock the TC in 4th if you're within that X range of speeds where the 3.7s torque is about 50 FT/Lbs too few to grunt it up the 2deg. hill for half a mile because youve got 300lbs of tools in the back or tires 2" taller than stock, or your vehicle is shaped like a loaf of bread (TJ's lol) throw a 2000lb trailer behind it and slow down 5mph under the speedlimit for safety.. and youre at 60-65.. annnnnnd therein lies your time-bomb a TC that unlocks at the cadence of a fat man snoring after a big meal. *pop*. 3d gear 1:1 locked via od off results in higher rpms and lower temps than unlocking 4th excessively
but that's the difference between an OD Off button, and a Tow/Haul button, and there is a difference. the KJ's have an OD Off button