Transmission woes

About 6 months after I bought my used 2000 Tundra, I started experiencing hard shifts from 2nd to 3rd. I read all the threads and found out this was a common problem. Some folks said they put in Auto-RX with good results. I purchased some and even talked to the man that invented the stuff. He said I may not see any results until I had the trans power flushed after 1000 miles running the goop. Well it appears my hard shifting is much improved, but the tranny seems to have developed a kind of growl but only in overdrive. Could something have dislodged itself and moved down the line? Should I go ahead and spend the $170 to get it power flushed, or should I put that money toward a rebuild or should I try to get a decent used tranny? What years are the trannies compatible (4.7)? Sorry for so many questions but this added to the needed timing belt/waterpump (89000 mi.) and new exhaust manifold (usual crack) has me a little strapped and I want to make sure I'm spending my money wisely. Thanks to everyone, you're the greatest!
Tundrabob58