94 Regal 3.8 Engine - Codes P0705 & 1406

[DJM1450]

I have a 94 Regal with a 3.8 engine with 87,000 miles. Every now and then the engine shuts off when I slow down to a stop. The SES light also comes on and off when I am driving. I changed the sparks and wires, but that has not solved the problem. I had the diagnostic done and the codes were P0705 (Trans Range Switch Circuit) and P1406 (EGR Valve Position). Is there a way to check out these parts prior to replacing them, because they are very expensive?
Thanks!