I bought my 2003 GMC 1/2 ton pickup new. 80 - 90% of miles are on the highway. OCI has been 5000 mi, using synthetics (M1 5W-30, GC 0W-30, Havoline Synth 5W-30, and PP 5W-30). Total miles on truck are about 81,000. Not sure when I first started to notice the lifter noise - maybe the last year or...