@GreenGO Juan
Did a lot of reading and according to guys who live breathe eat 12V Cummins…
Check my line pressure at wot in OD, locked with a mechanical gauge in the accumulator port. Note the pressure.
At my mild power level, I should replace the 2nd gear apply (kickdown) band strut and anchor because they bend when you increase line pressure to above 115 PSI.
Check the band for wear and if worn replace with a “slip in” band available a lot of places. You can replace it fairly easily in the truck when you’re doing the strut and anchor. Just dropping valve body gives access. I watched some videos and not hard.
Based on my measured before line pressure, turn line pressure regulator adjustment out (to increase pressure) 3-4 PSI per turn to get 120-135 PSI which will make the TCC, bands and clutches not slip and handle well above where this truck is.
Adjust bands, change fluid/filter and use Dex 3 or Type F (ATF4 they say is too slick) as they will increase clutch and TCC grip.
According to these folks, the above will make an otherwise healthy trans last a long long time at power under 250HP/600TQ
Bent Strut
Billet Strut and anchor in place
Also, I already knew the fluid doesn’t circulate in park position but they suggest letting trans cool in neutral (not park) after hard towing and also neutral for warming up on a cold day.