I find that when my hummer makes it past 70mph(after a long time of flooring it at basically redline) I noticed the steering goes from being basically factory new to incredibly loose. Does anyone have any ideas what would be the cause or where to check first?

 

Year, mileage, things done to it so far,make, etc...?

 

Do you do this often?

About the steering problem, are you sure it is not just speed vs after a red line run? If only this specific case, then I don't see how it could be steering mechanical. Maybe the serpentine belt/tensioner or PS pump is worn out? (Though that would make it overly stiff and not loose, right? Hmmm.)

 

2009, 154k, nothing has been done to it since I bought it

 

I do it whenever the highway turns into a 75 zone yes, I drive my hummer once a week though. it still has terrible steering when I've gotten to speed and the transmission shifted into 4th and RPMs drop.

 

Replace your tires! I've taken my 3 above 90mph many times and never felt loose steering.
Also make sure you shift to>>>D when driving at high speeds and never redline!

 

I'm always in D. and its not red lining per say but the trans certainly shifts down to 3rd(over 5k rpm) to get the power to speed up. The tires are pretty new(they are ling longs though :| )

if its not something super obvious I might just wait until I do a complete teardown of the car

 

From what you are saying, I can't tell if it has anything to do with how fast you get to 75, or if it is just being at 75. This is a crucial distinction.

I had a GM truck that would feel like it was shaking after a hard run (and RPM drop into high gear) because the engine would act up and made the truck feel unstable; it was not the steering or suspension.

 

Cheap azzed rice rubber with worn ball joints and shocks are always good for that.

Does it follow the traffic ruts on two lane blacktop?

 

not sure what you mean by traffic ruts. you mean the rumble strips? idk

I do know that basically any imperfection in the road will be felt in my steering and I have to counteract. Theres maybe 1-2 degrees of play in the steering