i've got the aforementioned crappy 4 speed auto that began life in my 2011 JKUr on OEM wheels/tires with the original 4.10 gearing and now runs 37s with 5.13s .It drives great but only if shifted a certain way because of the same issue that you're contending with( as-far-as your auto shifting too soon ).
I have an entire method of driving it that (even with a tuner compensating for the regear and accurate tire size, etc. ) I have driven it the auto like a stick; I start momentum forward in "1" until the appropriate RPM then a slight let off of throttle to shift to "2" after which of course comes "D" and I have driven it like this since day 1 , prior to 35s, since the beginning.The (They did not have the bumpshift option until '12 or '13 and) the 42rle has 'learned' to be shifted like that.
Otherwise , it shifts bam, bam , bam in auto and your in 3rd gear before you reach 35mp if you don't control it. I have verified that unless you jam the shifter - and who would do that- there is no detriment to doing this. It is the only way my 3.8l with auto 42rle can be driven and I do admit it drives as well as this setup can and performs very well now at 88k on odometer .
I take great care of engine and tranny but this one issue of having to drive it and shift thru those selections like a manual is obnoxious tho' I am oblivious to it by now.
I look forward to having an LS someday so that the tap shift option will be possible and I will have some real power and a tranny I do not have to coddle and pander-to like a special-needs child, no disrespect intended.
<edit: removed many run ones and bad punctuation-j_j)>
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Last edited by j3ff3ry_j33p; 10-17-2016 at 05:11 AM.
Reason: (Fixed a bunch of run on sentences and grammatical errors)