How do I troubleshoot these codes p0202,p1294,p2149 on a 2005 Duramax.

Question

I have had it at a dealer and they could not fix it, the problem has gotten worse. If i wiggle and mess with the wiring harness mainly at the two main connections I can drive it sometimes all day with no problem. Next morning won\'t run throws code, puts itself into limp mode. Almost seems like it is a broken wire or bad connection, have inspected and cleaned the connections.