Mickey Hrybenko

I need some help. I have a 2004 gmc sierra pick up truck with a 4.8. My question is I put a new transmission in new u jiont. My truck bands 15 miles per hour and fine after that. It will go a day or two then it comes back. If I let the truck set for a few hours it goes away. Then fine. Then it will come back . I can't get a straight answer from no one. Ever the guy who did the work. I was told to put special grease in the yoke also a grease fitting. I never had a problem like this before. Can someone please help me and point me in the right direction. Thank you for reading this who ever u are