It's a 1990 Chevrolet C1500 with the 5.7L (350) engine with throttle body fuel injection and an automatic transmission with overdrive in a stepside SWB "Chattanooga" custom pickup with 121,600 on the clock that now only averages 100 miles a month and is (almost) always driven at sustained operating temps. It is ocassionally used to tow an enclosed trailer hauling a motorcycle or whatever and may be used to do so on a long trip. It's presently in the first clean phase of an ARX treatment with SuperTech Synthetic 5w30. I just had to add about a half qt of oil after pulling a heavily loaded enclosed trailer about 200 miles...first time I can remember having to add oil. It only has 1600 miles on the oil and about 900 on the ARX and the oil has been in for over 15 months. Since it's no longer in "regular" use, I've dropped the Amsoil that it used for the last 30K miles (was on Havoline dino 10w30 every 3K since 20K prior to that when in regular use by my late Father). I was thinking along the lines of a HDEO (does this engine need the extra AW additives?) such as 10w30 Rotella or a HM 5 or 10w30, can't hardly find 10w30 Rotella around here....or do you think the SuperTech Synthetic 5 or 10w30 would do better and how long should it be left in service? I live in North MS where temps are fairly mild. Please give your recommendations and reasons behind them. It was my Dad's last pickup and I want it to last using the "best bang for the buck" oil and OCI....thanks in advance for your time.