sounds like you have a leak
try this,close the air inlet and if there still air going in, find the source, plug it and that should help.
I have plugged the air inlet and it stopped the air flow. I only did this for a second and wasn't checking for leaks so I will do that tonight. Thanks again Jose!

About your pump, if you've cleaned the wet end and you know that the impeller is in good shape and is turning easily on the shaft, there's not alot more you can do. You have to be sure to remove all traces of scale from the impeller and shaft, using vinegar or diluted muriatic acid. You probably know this already
yep.

your next step is to call little giant
I will do that. thanks for the idea!

If so, it's working, and I suspect what you feel is not air coming out of the venturi, but just some turbulence right around there.
I will check again.

1) What's the white fitting up high on the tube?
Its a second port to be used for counter current action. These things come from PM with a tee off the bottom port and the top port tied into the bottom. I think it's supposed to provide 50 gph of counter current flow. I guess the previous owner thought it worked better without it.

2) Where the output is, it looks like there are tons of bubbles; does this skimmer drain microbubbles into your sump? I bet there's an elbow inside the tube at the output so it draws from the very bottom of the tube, but it still looks very foamy to me.
Correct, there is an elbow. This is an older picture, the LG isn't creating that much turbulence or bubbles right now. It does drop some bubbles into the sump but they go behind a baffle.

Thanks for all the help Matt!