Rich is correct. On my pump there is an adjuctment that controls how fast the top lowers. Since HiLo used different pumps thru the years I can't say about yours. If I remember correctly that adjuctment is in the owners manual. If you can't find it get back here and I will look it up. On my pump there is an adjuctment to set the pump output pressure. Don't change this control as you can over pressure the hydraulic system.
Jim L & Faye
2003 Silvarado diesel crew cab
2017 Silvarado, crew cab 1500 6.2L gas w/ 8 speed tranny