RPMs high when stopped at lights, etc...also bad gas mileage (related?)
 

Lately I've begun to notice that my engine RPMs are hovering around or over 1000 RPM when Im sitting at a stop light, stop sign, etc. It doesnt do this all the time though, only occasionally.
When slowing down, I can tell the RPM is higher than it should be, and I can also feel a slight difference in braking (I also have to hold the brakes a little harder to keep the truck from moving, but not that much).
Earlier today, I put the truck in park when I got home, and the RPMs went up to around 1300...so I gave it a little gas and the RPMs didnt drop like they should...they hovered for a few seconds, then it would sort of jump down. This was the first time it did that, and I have driven the truck several times since then and it was fine.

Ive also been getting pretty crappy gas mileage (especially in town). I got a whopping 280 miles on my last tank (filled up with 24.5 gallons). Equates to something like 11.5 MPG. I can usually get 12 or 13 in town if Im careful. Dont know if this is related or not...

Any suggestions on where to start? I thought maybe IAC, but I thought that only affected the RPMs at idle (ie, out of drive).

Bttt

I had this happen when the alternator brushes started to give out. Check the charging voltage at the battery.

Your thought of it being the IAC is most likely it.