This morning i went out to start my truck, i stopped cranking after 5 sec. then i let the glow plugs cycle again, and it started right up the second time. Its been getting into the 30's at night and last night i just filled her up and put in some diesel kleen. I also changed both fuel filters last week. Any thoughts why it took so long? Usually starts right up even when 20 below. Almost like it lost its prime?