This may be a bit long bit but I want to give all info that I know.
I have a long commute to and from work in an 02 Impala 3.4 w/250k on it
and I do all the maint. Problem started to rear it's ugly head when I started noticing high engine temp. Knew it was time for a rad. flush and noticed that the over flow jug had a dark brown color to it. did the flush and also changed the thermostat. Now the radiator hoses are hard as rock after a drive to work, this may have been going on before I did the flush, which is another long story. What may be causing the hoses to be so hard after driving? I place a rag over the rad cap and turn to first detent to relieve pressure and it fills the overflo tank. where is the pressure coming from, no water in oil even after a oil/filter change .

 

It is a pressurized system. The hoses are hard because of the pressure. This is normal. Is it still running a high temperature? What is the temp it is running at? What temp thermostat did you buy?

 

I'm thinking it is a pressurized system as the radiator cap is factory 16lb. The temp now is in the normal range tho in stop and go heavy Denver traffic it rises above norm by a couple of notches. I have the base model Impala w/no tach and simple temp gauge.
After traffic is moving the temp brops back to norm. Before the flush and thermostat the temp was always (2wk) in the high side.

 

Oops forgot the factory GM thermostat 190

 

I love these cars this is my second one. First one was an LS with 3.8 drove it to 248,000 and then gave it to my son to finish off. This one is 252,000 and I do ALL maint.
love the ride and the 32mpg. I could go on all day about these cars. My other car is a 2010 LS Impala ,wife's car. I hate the outside mirrors on the 2010's

 

Are your radiator fans kicking on?

Do you have 1 or 2?

If 2, the first one may have died and the 2nd one is kicking in at the higher temp.

Can you hear them both run with the AC on?

 

Sorry took a time-out, No I didn't have to go to the time-out corner.
I turned on the AC and waited for a rise in the temp and yes both fans kicked on.
The temp guage displays 140 for the low and 260 in the red so I am assuming that the mid point is 200 and the fans kicked on just shy of the mid point.