Hard Torque converter unlock and sluggish

[94fourbyfour]

My truck just started acting strange today, I was driving down the interstate at 70mph and felt a hard, very harsh, bang in the drive line, the truck un locked the torque converter and would not re lock, about 5 miles later it locked back up, and another 5 miles it unlocked with the same bang and jolt. Also it feels very bogged down now when accelerating on city streets but does not feel like it is slipping, any Ideas?

Thanks
Dave