View mofishin's Jeep
As of 24 hours ago, I have the exact same problem as you, on the same model (Grand Cherokee (WK) Laredo, 4.7L, 545RFE trans,4x4). I drove the car about 20 miles in city traffic before parking in the drive for the evening. That night the temperature dropped about 40 degrees and continued to drop another 10 degrees in the morning. About 10:00 AM, I went out for a trip to the local wal-mart, and, like you, the tranny won't engage any gear forward or reverse. It's like the shift lever is connected to nothing. Also, like you, I have not had any indication of any kind of problem with this vehicle.
I do have a generic code scanner and it indicated a P0700 code pending, which would indicate a tranny issue. I cleared the code, but without an enhanced Chrysler tranny code it's pretty useless. I ordered a new code scanner today and should have it tomorrow. Hopefully it will provide more detail about where the issue may lie.
I'll let you know if I discover anything, or if a tow to the dealer is going to be required...