I'm confused. Is it that with your pump you can't get enough air in? Or, that you get the pressure on your pump up to 120ish and the air still isn't entering the tire?

Have you...

Tightened the exntender with a pliers?
Tried deflating the tires by poking the valve core inside the extender and then tried inflating from ground zero?

I would think this problem would be fixable without reinstalling the tires but I've also heard that plumbers tape is almost a necessity in the world of valve extenders.