distributor installation ?

You need to roll your engine over to TDC on the compression stroke for the number 1 cylinder. Then see if the rotor is pointing to the #1 spark plug.

I have to buy/replace a distributor/coil every 6 months because the distributor cap turns green and the truck starts running rough and stalling. Please help!

Something you might try is some silicone spray to seal things up and keep the moisture out. I don't think it will affect anything on these electronic set-ups and I know that it works on the older models before all the computer and electronic stuff. Something to check into, don't think it could hurt and would probably be a lot cheaper than buying so many caps and coils. Hope this works and solves you problem :D

Where should rotor be on distributor when on TDC?

Hello, I'm Danny.

Here is the information you requested. I've attached a picture below. Hope this helps and thanks for using 2CarPros................................
Danny-

Hi,

When you install a distributor, the rotor should point toward the number 1 spark plug wire when the engine is at top dead center (TDC). Here is a video showing how it is done:

https://youtu.be/El1H0_6IYxQ

Let me know if that helps or if you have other questions

Take care and God Bless,

Joe