transfer case issue

[70stroker]

First of all i would like to thank anyone who helps me fix my issues with my trasfer case.

Alright guys the truck is a 86 chevy 1/2 ton 4x4, The previous owner swapped to a big block th350 and a transfer out of a 79 i believe he said. They transfer is gears and not the chain style. I plan on posting a pic for proper identification.

My 2 issues with it are as follows.

1) 4 high works great. 4 low on the other does not. It does one of two things when you engage four low. Either acts like its in neutral and just revs, or engages and then when you put a good load on it then it revs. Like the other night i was pulling a buddy out and it engaged and i go to pull on him and its just revs like its in netural.

2) Not 100% sure this is the transfer but for sure sounds like its around the transfer/ transmission area. Going down the road you hear a hmmming sound. to me its sounds like gears whining. Now this is the first truck i had without the chain type transfer case, So is this sound normal for geared transfers or do i have a problem?

I checked the fluid, it is gear oil and doesnt appear to have any metals in it.

Again thanks for any help guys.