Your low oil pressure problems may be due to the fact that at freeway speeds the oil is unable to return to the pan fast enough to keep up with the oil pumps higher output. You may want to look at the oils that are used in the larger diesel engines, they are made to with stand high temps. I use a product called Premium Blue 15w40 (Cummins Blue) in all my trucks and cars(except the lawn mower my wife says it makes it hard to start). As for coolant I use the 50/50 antifreez and water mix, it work real good and if you lose coolant for some reason it is easy to find and replace, ie. auto parts stores, 7-11s even the supermarket carry anitfreez. Just one more thought, how are your radiator hoses?
