possible pcv issues
 

so when driving along about 50-55 let off the gas it seems to take too ling to come back down to idle. stays about 1500 rpm
noticed a air suction sound till it does finally drop. I have replaced the iac valve. it was making a chattering sound and would
idle up then drop to real low then about normal.

was wondering if the pcv valve would have anything to do with this. I noticed the hose was on the older side. maybe when warmed up
its choking out the vacuum that it needs.

trucks an 03 4.6

Sounds like a large vacuum leak from those symptoms, not a choked vacuum.
Have you checked the PCV hose where it goes into the base of the throttle body?
It's hard to see, but you may have a hole in the hose back there.
The hose is just plain neoprene hose and should be reinforced like fuel hose so it would last longer.

I second this. I had this same issue and it ended up being the PCV. I had a hole in one of the elbows. I replaced the entire assembly and it's been done ever since.

ill have to give this a check when the weather permits.

will the carb cleaner method work on finding a vacuum leak on this, (spray carb cleaner around if the idle rises thats the leak)

Think i have found my problem (possibly) the Electric Vacuum Regulator. This seams to be where my vacuum sound is coming from.
when i let off the gas when driving. (When i do it feels like the throttle is still open for a while)

It will but, - CC does too much damage to use. Not to mention, it makes holes in everything not metal. Worked well in the old days, when there were carburetors.
Nah, the EVR has nothing to with the way it runs, unless it's keeping the EGR valve open...but it's not. However they do get noisy, but you shouldn't be able to hear them with the engine running. Generally you can't hear the EVR until you shut the engine off. That's when you can hear them purging vacuum. This is normal.
This ^^^ is the most common fix. If your warm idle in park is above 750 rpms, then you can most likley find the leak by following the PCV line with you hand around it all the way to the back. They usually leak back by the firewall, the elbow as mandingo32 and R&TBabich posted above. A lot of time you feel the leak or plug it with your finger while the engine is running, idle will change, - there's your leak. These engines warm idle in park should be around 720-735 rpms...that's without leaks.

well it not idling high, somewhere between 700-800 at idle (after a 30 min. drive at 50-55mph) hard to tell exact number on the factory tach.
the only problem is when Im driving and it sounds like the EVR does when you shut the truck off.
when you let off the gas (like the throttle doesnt shut like it should)