What would cause my 4 speed to grind slightly when putting it into 3rd or 4th gear. If I hesitate before I put it into 3rd from 2nd, let the engine wind down a bit, it doesnt grind.

 

I'd start with a fluid change into a clean drain pan. Inspect what comes out, and run a good quality gear lube for about 100 miles. At the same time you change your fluid, make sure your shift linkage and clutch is properly adjusted. If it doesn't work better at that point, or there is a serious amount of gold flake in the lubricant you drain out, then I'd suspect syncros.

That's an easy transmission to work on. Go by the library and copy the section out of a Mitchell's or professional series Chilton's manual. They have great exploded views and take you step by step through the whole thing.

Good luck, and welcome to the forums.