NV4500 5th gear problems

Maybe a tranny specialist can help me. My wife just bought a 98 12v 2wd with a 5 speed. At first we had no problems for the first 2 weeks, then after a 1400 mile trip from Texas to north Carolina her transmission got stuck in 5th gear. I popped it back in neutral and we were on our way. I ended up draining the gear oil and replacing it with the oem oil from dodge and didn't have the problem again for about a week. Then the transmission got stuck in 5th and wouldn't pop out, so I removed the tail housing. I ended up replacing the 5th gear synchronizer and putting it back together. First drive after that it hung in 5th again. Could anyone help me figure this thing out. It has no problems with any other gear and the truck only has 134k miles. Out of every diesel I've owned I've never had this much trouble. Any help would be appreciated

Had this happen with a extremely worn 4500. A bottle of Lucas oil stabilizer band aided it until I could have it went through. It's rebuild time for the trans.

Either the shift fork is badly worn. Or the shaft splines are fretted enough to hang or the shaft splines are twisted.

Either way a fully splines main shaft and rebuild is in your future.

How consistently can you replicate it sticking? I'm wondering if you can do it consistently enough to remove the tailhousing and pull the fork off the shaft. I'm thinking there is a shift rail that's bent that's causing the issue.

I'm saving up for a rebuild with the updated mainshaft but for the time being I just told my wife to keep it out of 5th. When the truck is off I have no problem going in and out of 5th, just when I'm actually driving is when it gets stuck.

sounds more like spline issue if it only happens when the gear loads up.

My 2wd Dually with the NV4500 does that as well. It will stick 5th and not want to shift out if I try to shift immediately after stepping on the clutch. If I step on the clutch and wait about 2-3 seconds, it comes out normally.

When I put the new syncro in I was able to push it in and out of gear with my hand with no problem as well. The mainshaft liked like it was in fairly good shape.

I can't see the mainshaft being the culprit, since the gear that engages and disengages is on the countershaft.

The sliding gear is the one I was referring too. If it's on the counter shaft, so be it. Those are the splines I'm referring too. The sliding gear splines.

I had some trouble with mine getting stuck in 5th a few times, the last time it did it I managed to yank it out but then found I lost reverse, tore the back off the trans and found my problem was one of my sychro dogs for 5th/reverse kicked out and wouldn't let the sliding clutch go into the reverse gear.

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Check for wear on the shift fork shaft where it passes through the main case. I've been through well over a hundred nv4500's and this same scenario happened on two. Shaft wears a little lip on itself and hangs up on the main case hole where it passes thorough in fifth gear only.