Another CEL issue!

Hello all, I'm new to the site and I've got another problem with trying to read engine codes. I've read most of the threads concerning how to do this, but, none seem to work on this 540. I've tried the stomp test numerous times but with no luck. the light just stares at me. The engine has stalled out twice today and sometimes I get a hard down shift when slowing down with a rough idle. An ideas? Is there any other way to get the codes out? My local shop is asking $125.00 just to run a diagnostic.