I have a 90 XLT xcab 2.9 5sp 4x4 150+++ miles, truck runs great except for 1 problem. After driving at prolong highway speeds it starts a high pitched knock that continues until I get back to city driving/speeds then gradually goes away. Any suggestions on causing the knock ? Thinking maybe oil pump and/or clogged oil passages.

 

Hard to say. I've never heard of a description like that. Highway speeds does seem to be oil related though.
You could change the oil run the route again and see what happens.