Lml trans will hold better than lmm... also frame and front suspension is good bit better
frame is different, not necessarily better FYI. Fully boxed does not equate to better, careful with the kool-aid
I and many others prefer an open C channel. There is a reason the medium duty trucks are still running them
OP, not that you should listen to me. But I had a '15 LML that I traded for my 2008 LMM. I wanted more play money and the LML generational improvements didn't seem to be worth it to me. The LML does have beefier brakes and an "upgraded" hydroboost. Fully boxed frame doesn't really mean much other than tougher repairs if needed on the frame sections themselves, and less compliant ride from the frame. The front end is still needs the same mods, the driveline is much the same transmission aside, the shocks are still garbage, the interior is 99% the same. Some slight aesthetic differences on the exterior.
For me, the LML meant an additional $1,500ish on a CP3 conversion. That's $1,500 I would have to earn in addition in order to get the trans/turbo within the same timeline, not to mention most LML's were approx 4-5k more than a comparable LMM. The difference in price and not needing a CP3 conversion, allowed me to pay for and install all the mods on my truck this far without spending anything beyond what I had planned with the LML. At the end of the day I will be sitting at approx $42k with trans/turbo/deletes/tunes/sound system/aesthetic preferences/driveline R&R/new wheels/tires/built front end and good lube front to back. I paid $30k for my LMM LT crew cab with 50k this past March. I paid $43k for my 15 LML dbl cab LTZ and drove it for a month before switching to the LMM. Similar costs but in my opinion a vastly beefier truck.