Check engine light coming on, temp gauge rising, O/D not working properly. on 1992 Mercury Grand Marquis

The temp gauge rises to almost max in town and on freeway. Check engine light coming on for a long time but mostly pulling a hill. Transmission sounds like it is neutral when in overdrive. Have replaced everthing to do with the temp gauge except the sensor and the gauge itself. I really can't afford to play process of elimination with the repair shop prices so high these days.I have two different mechanics and they are both stumped. Check engine light goes off as soon as I get close to the shop, therefore I haven't been able to get it on the scope to get the code to diagnose the problem.At the end of my rope and my wallet. Please help!

by in Fortuna, CA on May 29, 2013
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1 answer 1 comment
ANSWER by , May 29, 2013
scan codes and post so we can adv
COMMENT by , May 30, 2013
The shop said that they can't scan it for the codes without the check engine light on, and it goes off right before I get there everytime. Otherwise I would be more than happy to send the codes. Thank you for your prompt response, I really appreciate it. Have a nice day.