1995 Other Toyota Models

I have a 1995 Toyota T100 SR5 4x4. The A/C has always been sluggish.You turn the A/C on high and it starts blowing semi-cold air. If I am moving down the road, the air conditioner air gets colder. If I just let the vehicle set it will not get as cold as when I am moving.I gauged the return line and it is 65#. I was going to add some freon/coolant/oil from a can I bought at Walmart that has a built in gauge inline, but the instructions on the can says 25-'45# in the normal operating pressure. So I stopped and got on this 'answer website.Any help would