More overheating ?s

[91GTturbo]

Let me know what you think is going on? I had the Ron Davis aluminum radiator and 180 thermostat installed on Wed. I drove the car Thurs and alot on Fri. No overheating at all. The temperature reads between the A and L on the NORMAL in the gauge. I only got on it a few times as I'm not sure how good the gas would be after the car has been sitting for 2 months. I did see 4 to 5 lbs of boost a couple of times. I only got into it (not even WOT) so some boost would build after the car had been driven for about 30 mins just to see how the temperature would do. It never got above A. I went out this morning to move the car and decided that I would take a short drive. I added about 3 gallons of Turbo Blue last night with only 1/4 of a tank left in it. Anyway as soon as the idle dropped this morning I left on my drive. Went out in the country where I could get on it a little bit, but still not to WOT. Built 4 to 5 lbs of boost again and let off of it. I drive just a little further and happen to look down at the temperature gauge and its at the last white mark before the 270 mark. I pull off and lift the hood, the radiator's not even hot. I sat for about 15 mins and managed to get it back to the house. What's going on, can anyone help? Thanks