2004 chevy tahoe with a/c issue

[mkwat18]

This past Saturday I had the a/c line replaced that goes to the firewall its the line for low & high side. Anyway we vacuumed it down and then made a mistake and put 3.0lb in instead of 2.7lb this has front & rear a/c. My issue is the a/c works great if you are sitting still but once you're driving it doesn't stay cold. I know the system is slightly over filled and would assume that might have something to do with it any help would be appreciated. thanks 

[asilverblazer]

Possibly the under hood temperature is lowering when traveling down the road allowing it to freeze up. Pressure switch should cut if off first...