need power steering help

[hfd410]

I swapped my 71 with a 5.3 and TKO600 5spd. It has around 800 miles with zero issues until recently. While bouncing off the rev limiter I lost power steering and the pump was howling. I have the stock LS power steering pump and stock but new gear box. I used the adapter fitting and detroit speed -6 power steering lines.
So I replaced the pump with new one, bled it correctly and it was fine at idle. As soon as I got on the road it started howling (new pump) and burped all the fluid out of the cap. I see where guys use the stock LS pump without issues or reducing pressure. Anybody have an idea on what would cause a stock LS power steering pump with stock style saginaw box to not get along ? Thanks in advance.