trans issue help please
 

i have a full built trans by goerand, the trans only has 8000 miles but was done in 2006, recently after coming off the high way it feels like my brakes are sticking, i believe it to be the torque convertor but am not sure when i put the truck in park and back into gear its back to normal, now after traveling down the road, just cruising fine, its like my trans starts slipping at about 60 mph then catching causing the truck to jerk, then going from 4th gear to 2nd causing the rpms to tach out, when i put it in park and turn the truck off then back on it seems fine, wat could it be?