Problem with 4x4
 

Totally happy with my 2002 F150. I purchased new and have 256K miles. No major problems other than routine maintenance. I have replaced transfer shift motor and vacuum switches under the hood.
These were done in past 5 years. My problem I need help with is, after using 4x high , sometimes I have a low roar after reaching highway speed(approx 55 and gets louder as I approach 70) also it has a pull tu the right which continues until I get home ,about 100 miles. After a day or two when I leave for my camp, its back to normal. Any suggestions??