First lets look at the walkers. They need to have risers on, the more the better, at least 4 per walker. Look down the big hole behind the engine. While you're in there, is there a curtain behind the beater and a second curtain a little further back? You need two curtains. On your 7720 they were made of metal and stayed. On the 50s they are of light rubber and eventually tear and go out.
Next, is your beater grate in the upper position?
If this is all as it should be you can change settings and put more material down on the big shoe instead of the walkers. Close your concave to zero and check that it actually is on zero and about to hit the cylinder bars. If the concave is not square in the combine and zeroed everything else is wasted time and money. Are your concave and cylinder bars in good condition?
Last speed up your cylinder as fast as it will go, at least 1000rpm, if you can do this without cracking kernels.
After all, in tough conditions you will still see some walker loss. But when I ran the 50s I never allowed more than 3 kernels on an area the size of a hand.