They're both tranny coolers. The lines run Tranny -> Rad cooler -> Aux cooler (the one up front) -> Tranny
EDIT: Overdrive and torque converter lockup are locked out by the computer when the tranny fluid is below 50* F. That's normal. As far as the t-stat, it can be changed without pulling that damn accessory bracket. It's a little tricky, and a bit messy, but I did change mine a few weeks ago and didn't pull the bracket. The bracket is an absolute PITA though, as I had it off twice over the summer (once to do the plenum gasket, then the water pump went 3 days later
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Call me crazy, but I actually try for mpg with this Jeep:
Typical driving: Back in Rochester for school, driving is 60 - 70% city