Saw this posted on T-nation. Having something very similar happen to me.

"So I tried to search whats going on with me in the past forum's but the problem is that I'm unsure as to what's causing this so I have a hard time searching it. (If that makes sense)

Here is some information to give you an idea of what's going on.

-Notice no imbalance during any type of dumbell or barbell pressing. The big movements.
-Notice slight imbalance or weakness of left tricep on smaller movements such as tricep cable extensions or 1-arm db extensions...etc
-When doing 1-arm tricep rope extension for example, I am in the same neighborhood strength wise meaning I can almost match rep for rep however the right fires really well and I feel the tricep burn deeply like it should, the left on the other hand is working but I don't feel anywhere near as much if any tricep activation.I have the exact same issue when I'm doing a lot of bicep exercises as well. So I can't blame just the tricep.
-If I adduct and externally rotate the left elbow into the body and make sure that my hand stays in line with the elbow as it tends to compensate by staying too far in the center (the hand that is) then I can hit the tricep.
-Sometimes when doing neutral grip chins or pull ups I feel tightness in the elbow where the humerus meets the ulna. (The pain is on the outside edge of the ulna) The weird part is this isn't always a constant, sometimes its not noticeable at all and other times its noticeable but not enough to make me stop the exercise just annoying.
-On a separate note i've also noticed that my left anterior delt near the clavicle seems tight at tights, mostly when I do reps above 8 for military presses or incline db chest presses. I believe this has something to do with it.

I'm not extremely worried about the tightness of the delt but more concerned about my left tricep not firing off properly because that could be extra pounds pressed on bench or overheads although I don't notice an imbalance during those exercises. Don't take this as I won't or don't want to work on shoulder mobility just wanted to let everyone know why I'm interested in getting to the bottom of this. I'll do whatever I have to get beyond where I am now.

Hoping someone else has had this problem before and can give me a heads up as to what's causing it.
Very grateful for all advice, thanks in advance."