I have a 2006 "LLY"/Allison 6 speed 4x4, 265s, & possible tune (unknown) with 348k on the clock. I've noticed an odd shift between 3-4 (+/- 30 mph) shifts under 2000 RPM. Yesterday I drove in "M" for the shits n giggles and the same 3-4 shift was just fine. Is this possibly a tune issue in the trans? Don't have a code reader capable of reading trans/tcase codes so no info there. Fluid levels fine, spin on and internal have 3k till change (I change them every 15k, or that's my plan if you could help on that as well). Thanks