High RPM at 60mph. HELP!

My 86 cherokee 2.8L. is showing 3000 rpm at 60mph. I think thats kind of high, but I need an expert opinion. the engine is starting to get a low end rattle at thoes speeds after warming up. I thought the converter might be bad because when I swaped engines a few weeks back, I was removing one of the bolts holding the flex plate to the converter, I got covered in tranny fluid!!! the tranny is a 904 auto. and I think its got a lock-up, because sometimes it will get to 45mph the rpm will drop from 2500 to 2300, I think with lock-up it aut to be more of a drop than that.

anyone have ideas before I go speending money taking it to the mechanic shops!!!