Gertrag noise- problem in Colorado !!!

[19Kgvw]

Long time TDR member....just don't post much unless needed.

Long story short - I'm half way on vacation with my '93 CTD with the 5 spd Gertrag. The trans has 143K and I've owned for 10 yrs. I've change trans oil regularly (every 15K) with 4.5 quarts of 5-30 synthetic plus I have a additional filter off the PTO.
Problem- this morning I noticed a "growl" at 35 and higher. I stopped and checked the transfer case and added .5 quart. That was Provo Utah and so kept driving - in Moab UT, I stopped because the growl was still there and there was heat on the shift lever that was abnormal.
The growl is dependent on speed....ie the growl doesn't change as I shift or coast with the clutch in and the trans in neutral.
In Moab at a shop we put the rear on jacks and ran the driveline. The rear diff was quiet and not abnormally hot - I do run a Magtech cover and the fluid on the dip stick was normal.

There was more of a grinding noise from the trans than the transfer case when listened with a screwdriver on the cases.

I'm in Cortez CO right now (I'm from Seattle area) waiting for a shop to open in the morning that was recommended by two 4x4 shops in Moab. My understanding is that they have knowledge of Gertrags.

I'm thinking that it could be the output shaft bearing going out....(is there a 5th gear nut problem with gertrags?? I thought that was NV4500). If the output bearing....can that be replaced?

I really didn't want to drive much further without getting it looked at as I didn't want to get stuck alone side the road. I've put 350 miles on it with the noise - do you think I could do another 2000 back to Seattle or is gonna puke on me???

Is there any other potential problems to look for tomorrow?
and.....if a new trans is the answer, I would want to think about the NV5600 swap that was popular a few years ago- is that still an option to do??

thanks for any help - Rich (stuck in Cortez )