Transfer Case Problems

I have a 2002 Silverado 1500 H.D. with a 6.0 litre engine. The transfer case is a NP8 New process (4-button). Here is the problem. when going down hills and trying to hold the truck back without breaking and shifting into a lower gear it sounds like 2 gears are mashing together coming from the transfer case. The truck then no longer holds back and acts like it is neutral mode until you hit the gas. This happens basically all the time when there is a load on the truck or pulling anything. Have had the transfer case apart several times and everythime the nylon pads on the shifting fork is damaged, have had several shifting forks installed but the problem still continues. Any help or suggestions on this matter would greatly be appreciated.:banghead:

I have a 2002 Silverado 1500 H.D. with a 6.0 litre engine. The transfer case is a NP8 New process (4-button). Here is the problem. when going down hills and trying to hold the truck back without breaking and shifting into a lower gear it sounds like 2 gears are mashing together coming from the transfer case. The truck then no longer holds back and acts like it is neutral mode until you hit the gas. This happens basically all the time when there is a load on the truck or pulling anything. Have had the transfer case apart several times and everythime the nylon pads on the shifting fork is damaged, have had several shifting forks installed but the problem still continues. Any help or suggestions on this matter would greatly be appreciated.:banghead:

The oil pump system in it may not be working good.
What no transfer case is it?
MT