Unfortunately, most likely yes. Synchro failure I assume (clutch ring/stop ring), though other problems can contribute.
You could try changing the oil, but most likely will find lots of metal particles. Unless you want to tear down the 4500 yourself, a rebuilt one will run ~ $1800 last I checked. Try Standard Transmission & Gear, Ft. Worth. They have HD 4500's w/updated full splined shaft to help eliminate loss of 5th gear, as well as parts and rebuild kits. Parts to overhaul my 4500 ran ~$300, but I did all the work. NOT recommended DYI unless prior tranny experience, and enjoy pain...
www.standardtransmission.com

Sorry, wish I had good news.
-Scott

ps -photo of synchro linings (clutch rings) attached ...

 

[quote author=97Dually link=board=16;threadid=10634;start=0#101700 date=1044586336]<br>Is the problem the same if its intermittent going into ONLY 3RD?<br><br><br>TJ<br><br>[/quote]<br>Maybe not. I found my 3-4 hub was installed backward from the factory, which can cause hard shifiting. Also, the shift sleeve can be installed backward (easily) which will do the same thing. Could also be synchro stuts/springs, but I would guess one or both of the following: Worn roller bearings in 3rd gear (or even worn journal), and excessive endplay on the mainshaft. That allows the gear to ride cocked, and probably causes synchro problems if bad enough. You can set/check endplay by pulling the extension housing, and 5th gear, then the bearing retainer, but everything else will require pulling the tranny out. If you hear lots of &quot;gear noise&quot; when accelerating in 3rd, probably bearings/endplay, IMHO.<br><br>Just my .02... not a tranny expert, just spent way too much time under mine.<br><br>Reagrds,<br>-Scott