I have an 85 which acts similarly. Having had conversations with Ranger owners, & reading a number of forum posts, it seems that the OE oil pumps used in Ranger engines are barely adequate. After significant wear from high mileage (or abuse) occurs in then entire engine (not just the pump), it can no longer keep up with the demand. It is accentuated when it gets hot, because the actual viscosity of the oil drops (even though it is multi-vis). Other individuals who know more about it than myself have strongly suggested replacing the stock pump with a high volume pump. Until you find the time, money, & enthusiasm to replace the pump, you can "band-aid" the situation temporarily. When you're ready to change your oil, BEFORE you do, start the engine cold, and pour some crankcase flush in SLOWLY while it idles. Let it idle at least 15 minutes, DON'T DRIVE IT! Then, drain the oil pan as per usual, but put a higher viscosity oil in (like 20W-50). The next time you drive it long enough to get good & hot, observe its behaviour. If the oil light still wants to come on, and/or valve noise occurs again, add a little STP oil treatment WHILE IT'S HOT & RUNNING! Don't add it to a cold engine! If one bottle of STP doesn't do it, you COULD slowly add a second bottle, but try to avoid it if possible. You don't want your cold start viscosity too high.