A new failure mode and I've tried them all

My wife is out of town for the week so I borrowed her 97' 4.0 automatic to drive to work today. I live about seven miles from work and the sucker worked fine (well for a tired lifted Jeep, fine). Got to work and left the keys in the ignition like I always do with my cars. Got done with work, hopped in the rig cranked it over and she spins but doesn't start. OK pop the hood check all connections check fuel pump check fuel rail . All the sensors on this truck are less than a year, all tune up parts and coil are recent. The truck has never failed to start even with serious problems outstanding. I unhook the battery for a few minutes and when I reconnect she starts right up and runs well...

The only variable I can figure is that somehow leaving the keys in the switch somehow pissed it off. I only have three keys on the ring so there was no real weight on it. I didn't leave it in acc or it would have been dead. Any Thoughts?

You could have had a "less than tight" battery connection, which would explain why it worked when you hooked the battery back up (and made sure it was tight).

Just a thought

Nope, connections were clean and tight. I baking soda ed and vaselined the connections when I took off the winter wipers.

Nothing to suggest...but did your 97 have the 'chip in key' system? Any 'security' lights on the dash blinking or on?