4X4 PROBLEM URGENT PLEASE HELP!!!!

[500hppsdiesel]

i have a 2004 f250 with shift on the fly 4wd! the problem i am having is that when i turn the switch to 4wd it goes in with no problem. shortly after i engage the 4wd it acts as if the hubs are engaging and disengaging sparatically and the 4wd only works half of the time. not only does this happen but also when i go to disengage it with the switch it will not disengage it stays in 4wd. the only way i can get it back into 2wd so that i can drive it is to crawl under the truck with both leads of a battery charger and pull the plug off of the transfer case motor and make it go back into 2wd with the battery charger on the plug of the motor! i have replaced the transfer case motor along with the vaccum selenoid under the hood and i still have remained unsucessful!!! i have also checked all of my fuses. can someone with more knowledge of this situation please give me their input as to what the problem could be. any help is greatly appriciated

[500hppsdiesel]

Heres a little update!! Took the truck to a mechanic yesterday and come to find out there is an auxilary relay box on the driver side under the hood that controls the 4wd!! Replaced these relays and all is good!! Just a little info in case someone has this same problem!