My trucks doin about 1690 RPMS AT 55. is that over drive? I'm not sure. Can I just put my truck out of over drive right when I get it and click the button and not use it at all?? I know There's down siides

 

What year, what engine?

 

It's a 02 with the 5.9 360

 

Overdrive is running about 1700 rpms at 55 and then when it gets wet out It drops to 1400 and bounces around. This is a 02 5.9 360 with the 46re

 

The problem is most likely going to be your throttle position sensor. As crazy as it sounds it will cause a surge at highway speeds even if it doesn't do it at idle or below highway speeds. My sisters 2001 Durango used to do the same thing. $25 and you're set to go!

 

For what its worth my 97 has a 360 with the 45RE trans and I could do about 1700-1800 Rpms at 70mph.

Should be the same setup as yours.

 

Now my truck only does this when it's wet. The tranny rpms will hop all around in overdrive ONLY when it's wet out and will go down to 1400

 

It's only doing this when it's wet out though

 

You never know it could be just a coincidence that it does it when its wet outside. I would say if you're having a surge of any kind get your hands on a different throttle position sensor, or at the very least try to re-calibrate yours.

Are you using cruise control when it happens? Does the speedometer appear to bounce or seem notchy or abnormal in any way when accelerating or decelerating?

You're going to have to check a few harnesses for wetness & corrosion to see if they were compromised. Start with the speed sensor on the trans, then the abs/speedometer sensor on the rear differential. Also check the 2 harness connections behind the drivers side front mud flap. The speed sensor on the trans only gives the pcm a reference of speed for shift points, it doesn't lend any information to your speedometer as only the rear differential ABS sensor does that.

Without driving your truck its kind of hard to diagnose, it could even be a torque converter lock up solenoid. Any more information about symptoms would be great. Take it to a car wash and take a video of the way it runs after.

 

Sounds like a good idea. My Speedo is in good good condition and all of that, the over drive solenoids and wiring harness are all brand new...so is the speed sencor. Next were gonna try some wiring and try TPS, Thanks