95 Rodeo first tune up

Hi all, this is my first post. Excuse the bad english, is my second language.

Recently I bought my first Rodeo (1995, 3.2, 5sp, 2WD, 160k) in very good conditions. The main detail that convince me to close the deal is that the engine doesn't make the "Tick" a lot of users mention in this forum and, in all aspects, this truck looks very well maintained and cared.

My first concern is how to keep this baby running without the "tick". I bought it from an used car dealer, so I don't have any info of the first owner (I'm the second) so I don't know the kind of oil used (dino or synt) and the OCI. In the first close inspection, I found nice Bosch Platinum 2 spark plugs, with some wear (will be replaced), the oil looks clean and is at the Full hole in the dipstick (will be replaced, the filter too), the coolant is in good condition too (maybe will be replaced, I'm not sure now).

I'm looking for your advice in this areas:
which parts do I need to inspect closely/replace right now?
I live in Reynosa, south of the border, near McAllen, Tx. so we have a very hot summers (100F) and cold winters (28F) and the truck has 160k miles. What Oil brand/viscosity do you recommend? I use castrol GTX 15w50 (I think so, my memory is sooo bad) in my other ride (contour 1998, 2.0 5sp, 190k) without problems, but I know a truck is a very different beast.

Thanks in advance!

BTW: I'm a newbie in the Rodeo stuff, but If you need help with computers/IT issues, let me know!