1996 peterbilt 378 grinding/vibrating noise?

1996 peterbilt 378 3406e cat 18 speed eaton. 4.56 rockford rearends.

Heres a long story somewhat short.
4 montgs ag9 had ujount break on a tuesday. Replaced and rebroke on that friday. Found bad yoke where it broke. It was the driveshaft going into the first differential. So rebuilt with new yoke and 2nd new ujoint. Last week the same ujoint broke for 3rd time. So replaced yoke on differential with 3rd new ujoint. Also found carrier bearing just gone. Could move driveshaft up and down an inch. So replaced it also along with new yoke on front driveshaft going to tranny.

Ive had this grinding/vibrating noise going on before my ujoints started breaking. I know its something to do with my driveshaft area i jyst dont know what. The noise only happens with a load. Not empty or bobtailing. When the noise happens i can feel in throttle. It randomly happens between 55mph-70mph but will go away when take foot off throttle.

I really need help figuring out this issue. Cant keep affording the tows and driveshaft repairs.