Confronting the problem of the hard to rack slide on my Beretta 81 I decided to look at the problem from every angle - the first thing that occurred to me was that the actual force required measured in lbs. was very little, in fact it was only a fraction of the effort required to draw my 80 lb bow, which is a similar movement to racking the slide and uses pretty much the same muscles. The actual force required could easily be achieved by a moderately fit 100 lb. person! I tried using different grips and techniques and positions - I found I was the strongest with my 2 arms extended skyward at a 45 degree angle to my body, but this only made it slightly easier to rack and is certainly not a practical posture when one has a gun in their hand. I concluded the problem was not with me but with the gun design.
My Beretta Cheetah is the early B model, so the following factors contributed to the problem : 1 - The blued finish created a very, glossy, slick surface on the slide. 2 - Unlike the later F models the slide serrations extended only half as far (just 1 inch long) and with no second set of serrations at the front of the barrel. 3 - The 81 are 84 series are a double stack design which means the grip is wider than the the slide, making it impossible, using the overhand grip, to achieve solid contact and pressure with the palm of the hand. This is made worse by the fact that protruding even further than the grips are the slide release and safety levers, both with sharp edges. The top of the grip also has a lovely sharp corner. This can all be confirmed by the fact there are cocking aids that fit over the front barrel making it easy for the left or weak hand to get a solid grip and taking the effort out of racking the slide. So the problem is this: the weak small muscle groups of the fingers and thumb trying to grip a very non-ergonomic surface.
Experimenting, I did find a technique that is working for me, but perhaps not for everyone and may raise some protests from a safety standpoint, though I don't see why. Standing with my feet about a foot apart, arms hanging down, gripping the gun with trigger hand, the weak hand with a thumb and the base of the forefinger (slingshot) grip on the slide and barrel pointing down towards a point on the ground to the left of center and out in front about ten inches - sharply thrust down with the right (dominant) arm while keeping the left arm slightly bent at the elbow and concentrating its strength in gripping the barrel. The energy comes from straightening the right arm, but I found an even better effect came from keeping the arms straight the entire time and in a teeter-totter motion sharply dropping the right shoulder while simultaneously raising the left as if the shoulders were fixed to a pivot point at the top of the sternum.
There is one other trick I want to mention, but first a question - Common, I think, to mostly earlier Berettas, at the front of the slide, about a half inch back the slide begins to flare out on both sides of the barrel creating an indentation. I don't know its purpose other than for saving weight where the extra thickness was not needed, But it makes a very grip-able shape for the left hand thumb and fore-finger grip - I found it provided a better gripping area then the slide serrations did, making sure, of course, the fingers stayed clear of the end of the barrel.