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.