need transmission advise FAST

[carlover]

I just bought an '86 560SL with 62K miles on it. The owner was in her 70's and never drove it much so I doubt if this problem ever came up during her ownership.
When I really "stand on it ", it jumps back into 1st gear which would be fine except it tries to go into 1st at 55-60 mph. It goes into second and then into first, and if I hold it on the floor, it won't come out of first. It starts "bucking" like it is going in and out of gear. The normal shift pattern is fine. It goes through the gears perfectly. This is only a kick down issue. If I let off the gas slightly, or if I don't mash it hard against the floor, it seems to be o.k., except doing that means I'm not getting full acceleration. I assume that the kick down is electrical, and if thats true, I hope someone can tell me how to adjust it properly. I can see an electrical plug in the side of the tranny, but don't know if that's the kick down or not. I didn't see any mechanical linkage (other than the shifter) so I need some help with what to adjust. NO, I don't slam it against the floor often, but want to be able to do so without causing any damage. Any advise/help will be greatly appreciated.
Thanks in advance
Tom