I stopped by the dealer. He thinks it's my running boards but didn't hear anything. It was doing it before I put on the running boards. I thought it could be something aerodynamic related as it happens at speeds over 55. Now today it's doing it at speeds as low as 35, a speed where air should not be a factor. It's happening most of the time now, so maybe I will take it to the dealer and he should be able to hear and feel it this time. When it first started, it happened for a few seconds at a time. Then go away. I thought it could be a bad tire too, but it happens like an on and off switch. I guess the more it happens, something will happen then we'll know what it was. I've felt the hubs, cool. checked underneath for something loose. All easy highway miles, no pulling as yet. When I do find out what it is I will certainly post the results back here. Absolutely great truck, she just has a little gremlin lurking somewhere.
Mark thanks for assistance. Makes me feel good to know you care.