After much reading and recommendations from you guys I made the switch from 15w40 to 5w40. Now when my truck is cold it fires up really rough. It seems like it over revs and misses and acts ups for about 5 seconds before it settles down. Both of our shop trucks are stock 6.0 with 15w40 and they fire up great. Mine just started doing this since I changed my oil. It seems like the basic mods I have done to "help" my 6.0 last and run better have only caused me problems. My truck ran better stock.
Any help or ideas?