Rpm Jumping While In 5th?

PrincessOfNohr

New Member
Jul 12, 2016
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I recently bought a '07 V6 Mustang convertible (she's my baby), but I've noticed something a bit odd while I'm cruising. After I've been traveling in 5th gear for a little bit, the RPM will go up slightly and not go back down. For example, it's initial upshift RPM into 5th at around 45 mph is about 1250, but after a few seconds, it will jump to about 1500 and stay there. If I hit the accelerator to downshift, it will go back to 1250 after I get back into 5th, but soon goes back to 1500 and stays at that level.

I'm not sure if this is a normal thing for these cars, or if it is a transmission or voltage issue? I got the battery tested and it seems it isn't charging all the way (at 585 vs 740), so I thought it might be the alternator trying to kick in to recharge the battery? We have Ford buses at work that do something similar with high idle, but I've never been sure if this is present in smaller vehicles. The other option would be that it's a transmission-related problem, which I really pray it isn't.

So am I close, or way off? Is this something to be worried about? Any help would be appreciated!
 
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