First off this is not the truck In my sig. It's a late 99 f350 4x4 7.3. My issue is that my truck seems to rev up and then back down when im giving it gas. It usually happens around 30mph and 1k RPM and itll shoot up to 1.5k and then it will go back down then back up to 1.5k. What seems to happen is that when im driving back roads and take my foot off the pedal when i get back on it it shoots right to 1500 and wont accelerate but then almost immediately it will go back to 1k. Truck also will stutter and shake.

Almost feels like when the rear tires are slipping and the engine revs. Then the tires finally catch there's that bit of shaking and the rpms go back down. However I know my tires aren't spinning.

-started 1 month ago, at the time I also found my rear diff vent tube disconnected from the axle
-only happens in snow or rain so far
-O\D light is blinking
-Only happens when truck has been running for a few hours
-I've put about 5k on the truck since I got it. O/d light always flashed but the truck always shifted fine.
-truck runs fine about 95% of the time but like I said when it's wet and the trucks been working I can barely get the thing over 20.
-there seems to be a threshold of like 25-35 moh where if I can make it past that the truck is fine as long as I don't go back down below it.

Thanks for your help, I'm puzzled

 

Well the very first thing you need to do is get the codes read. With the OD flashing that means you have transmission trouble codes stored. Now you will need a good scanner to read them the ones at the auto parts stores will not read trans codes. Get them read and post back what you find and Mark are resident expert can help from there.

 

Completely agree with this.

I don't think it has anything to do with your rear differential though. Nothing in the rear diff is going to cause a variation of your RPMs; either it works and is connected or it isn't. There isn't anything back there that can slip and still provide power.

 

Okay il look into it. I just thought it odd that it started happening As soon as I found the vent tube off.

What type of scanners will read transmission codes and how much $ are they? I figure it might be worth investing in one

 

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