Another additive to try if you're bored is marvel mystery oil. The 258 in my dads jeep had horrible valve-train noise and once he started running that through every other oil change it quieted it down quite a bit. It's supposed to be good as a trans/motor cleaner and additive so I assume it's just got a ****-ton of detergents and lubricating agents in it.
I also notice that when I switched from conventional to full synthetic my first 2 oil changes the oil was black within a week, whereas normally it'd take a few months. It also quit leaking a quart a month and now only needs one every 6 months (I refuse to put a main seal in from under the truck).
And DO NOT let jiffy-lube service your vehicle. Your time to change it is good therapy and you know whats going into it. I caught the assholes here putting conventional in a company truck when the company always pays for full synthetic. Easy way to get your profit margin up. Along with not changing the air/oil filters which we've also had problems with.