I saw you have 2 posts the same haha. I will say between 600-900 once again. Its vague but I do not know what it is for your truck exactly. I think 900 sounds like a good answer

 

Ha ha, yes I was working on the truck tacho when I posted and needed a quick reply....I know I shouldn't post the same thread twice but I got carried away lol

I've looked online and for love nor money I can't find it, but am guessing around 900, that where I've set the needle for now...if I hear different, I'll change it.

 

That would be a safe bet, I think mine runs around there too.

 

I just checked my manual for you: A 5.2L V8 Automatic tranny----idle is 700 rpm manual tranny is 750 rpm

 

Mine idles at about 750 with automatic trans.

 

Update on Idle speed

Just thought this info might help others.

Took her to get inspected yesterday, of course she passed, but under idle according the diag machine print out, she was idling at 640 and was fully warmed up.

She's a '99 5.2 V8 Auto 2wd with 207500 miles on her.