on demand 4wd conversion? Front diff vibration.. HELP!! - So i'll start from the beginning and try to make this short, I have a 2000 sierra 2500 4x4 and a ...

So i'll start from the beginning and try to make this short, I have a 2000 sierra 2500 4x4 and a few months back blew a brake line and replaced them with ss lines. After bleeding them my ABS light and 4x4 light were both on, Took it to my friend at a gm dealer and he said the abs unit is bad and its linked into the 4x4 so that doesn't work either. Since i have a manual shift transfer case i got a wiring diagram for the actuator figured out how to engage the front diff but I've tried every possible combination of wiring i can think of and i cant get it to retract. So after doing research i found a "4wd on demand" conversion plug that eliminates the actuator and engages the diff permanently so i figured just leave my actuator engaged and it would be the same thing. I have a very slight vibration at 75+ which is to be expected BUT now after 3 months of driving with no issues i now have a intermittent vibration that sounds like a wheel bearing but with a lot deeper tone... Now i work on cars very often and have changed many wheel bearings and axle/cv shafts before and never had one that was intermittent so I'm thinking that's not the issue but there is a first time for everything. I talked to an engineer at Eaton that does destructive testing on these axles and even he is baffled. Also it makes no difference weather i engage the 4x4 or leave it in 2wd.

So my question is: 1st off has anyone ever done this "4wd on-demand conversion" before? And what would cause an intermittent vibration in the front diff?

I'm also in the process of removing the differential actuator and changing the fluid to see if anything changes...

So you are driving on dry pavement with 4 wheel drive, ALL THE TIME?