You absolutely need a very competent tech doing all the checks necessary to ascertain to a certainty what and where the problem is before replacing any parts. Many people have reported having their trucks 'fixed', paid a goodly sum for the fix, only to find that their trucks really aren't fixed.
If you follow the prescribed sequence of operations outlined in my previous post, many of they tests are quite simple and can be done with a simple volt meter and do not require an expensive tech. Some may be beyond your capabilities or desire to learn to do the tests. You will have to decide which is best in your situation.
2008 Silverado LT, CCLB, Edge Insight CTS
2009 Arctic Fox 29-5T, Silver Fox Edition, Onan 3600 LPG generator