The roll backwards is done in the torque converter. There is a one way sprag that only allows the driven shaft into the tranny to rotate in one direction. So I would suspect that the problem is there.
The clunk sounds like there is a lot of play in the tranny gears. Some amount is normal but how much I am not sure of.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k