if by "whole range of motion" you mean doing dumbell military presses and lowering them till your arms cant go any lower, that is your problem. You should come no lower than 90 degrees at the elbow (some will say slightly further) But if you are lowering the weights till your elbows are hitting your obliques, don't. You will feel that something is sliding back into place becasue you are putting undue pressure on the triceps tendon (as well as others) when performing full ROM. When you start to push the weight back up, the tendons are so stretched they have less strength, causing the pain or sliding you are talking about. true strength does not come from the ends of lifts, ie, the full extension or contraction of a lift. if it stops with lighter weight, it seems to me that you are lowering the weights too far and aggravating those tendons.