trying to 100% finish my 65 chevelle need help

[94snglturbo]

Hey guys. i have been driving the car a few hundred miles since we did the ls2/turbo/4l80e etc and it runs great. i just recently changed my stock 65 gear box to a quick ratio gear box but for some reason when im driving the car feels good but as soon as i start to hit the brakes the steering gets really stiff. does anyone know the problem of this? i have a agr power steering pump that was new when motor was installed and worked great with the stock 65 gear box. i have the stock brake booster in no proportioning valve. 4 wheels dick brakes. which all this stuff was the same when i had the stock 65 gear box. any help would be greatly appreciated.