1969 Ford Truck broke something in my tranny?

Transmission problem
1969 Ford Truck V8 Two Wheel Drive Automatic? Miles

c6 transmission, 360 v8 9" differential. Unsure of the mileage, but runs like a champ. Seattle to orlando, to jersey, to orlando, back to jersey, zero problems. New house here has rediculously sloped driveway. 1k lbs of crap in the bed and another 2k in a uhaul trailer. Backed it in reverse up this driveway and had to manuever along side the house, took 20 minutes. Truck was going nowhere, and made this hopping feeling. Now after the incident at 50mph if I cruise or let off gas it feels like driving over the wakeup strips on a highway, rumbles and shakes the whole truck. Under hard accel its fine. At 800 rpms idle in drive let off brake and she rolls on her own just fine. Shifts fine too. Around town shes fine, just on the highway 50mph and above when cruising or deccel, god aweful noise and vibration. Thanks guys.