all answers USA on USA cars,only. (exports are diffr)
so if you didnt scan it when it fails, how would you ever find the truth? (if no errors. then it can be pure mechanical failure)
the car has TCM a tranny brain.
its covered in the SM, read that chapter yet.
on newer cars if the Tranny overheats or engine both can go to LIMPHOME< but your car is not even close to new, is it?
Jeep calls that LIMP-in.
my guess (sux) is its the 4.0L engine with matching AW4 box
Aisin-Warner
it wise to know whats there first. before trying to understand it
a FACT !
so did you google search AW4 boxes. , i bet not.
but they are unique. as all different boxes are.
is the CEL lamp glowing running, Check engine lamp
PDC fuse 16 ok (4L,aw4) TCM power, must be good at all times.
is the throttle valve cable to transmission stuck out?
if it does, the TCM and trans will either go nuts, or shift way late.
http://etereman.com/blog/fiat-transmission/the-popular-aw4-automatic-transmission-and-common-problems-associated-with-it
the TCM shifts using solenoids, we check that the signals to said solenoid actually do go to the correct voltage levels
in to 3rd. (you said stuck in 2nd)
if that is ok, then the TCM did it job and the problem is INSIDE the box. end story, we use remote test meters to monitor wires driving.
chapter 21 and 8w are free to read here any time you wish
posted over 300 times the Jeep Bible (SM)
http://www.morris4x4center.com/knowledge-base/index.htm?utm_source=cj#service
click XJ