70# and 80% letoff doesn't matter much. The amount of letoff doesn't matter. You still have to roll the cams over that 70# and that can tire muscles out quickly. Try it this way. Hold your bow out as if to aim it and draw the bow stright back to your anchor. If you have to struggle at all, even the slightest bit, then the peak weight is too high for you. You should be able to look at your target and draw the bow stright back to your anchor, never moving your head. You should be able to draw the bow to YOU, not move anything. Otherwise the bow needs adjusted to fit you. Another thing that will cause your problem is that maybe the drawlength is too long also. It could be a combination of drawlength and weight.
Some guys shoot their bows at a specific weight during the summer and then increase the weight for hunting. IMO based on experience is that this is doing things backward. While practicing and shooting 3D you have the chance to warm up your muscles which cn allow them to draw more weight. Sitting in a treestand waiting for a deer to come along, maybe for hours, you don't have the option of keeping the muscles loosened up. Drawing that bow the first time might be a real struggle. If it is then the bow is turned up too much. I actually drop mine down between 5 and 8 lbs for hunting from 60-61 to the mid 50's. When the arrow passes through the deer and sticks in the ground they don't seem to care what the bow was set at. BUT I can draw it.