97 F250 keeps blowing off the low pressure return line off of the pump, what is wrong?

Did you bleed the system??? You might have an airlock in the system. When replacing any power steering component on a vehicle, make sure your clamps and connections are tight and nothing is kinked. Did you connect the lines correctly??? There shouldn't be any amount of pressure on the return line to blow it off the pump. Also make sure you didn't over fill the pump resevoir. There is a line on the side of the pump filler tube that reads full when hot and full when cold. You should have filled it only to the cold mark. Then you have to cycle the steering (bleed the air out) by turning the steering wheel all the way to the left, then all the way to the right back and forth a few times with the power steering pump cap off of the pump and the truck running in Park, this will bleed the air out of the system. Then replace the cap and recheck your fluid level, once the engine warms up, the pump should be full to the "hot" line and you should be good to go, otherwise your gearbox might be defective. On my Ford Crown Vic, I went thru 3 gearboxes from Chicago power steering before I got one that was rebuilt correctly. Good Luck, Kenny.