1995 2500 with cummins. while driving down freeway at 60 or so it will shift back and forth from 3rd to overdrive. flat, up, down, the grade doesn't seem to matter. Probably about once a mile. I have over sized tires(was bought that way). changed fluid and filter, seemed to help a little. was wondering if the over sized tire was confusing the ECM or do I have a trany problem. any thoughts would be great.

 

sounds like either a valve is sticking, the pump is not able to build enough pressure, or you have a piece of trash in the system

 

Thanks for the input. I think I will try to flush the trany.

 

Are you positive its going from OD to 3rd or is the torque convertor just jumping in and out of lockup?

 

Think it is droping into third the tach seems to go to about the same spot as when I push the OD off switch. What would the lockout act like???

 

Well when the TC goes out of lockup it probably wouldnt be as firm as a downshift and the rpms would be slightly lower than 3rd gear. The reason I asked that is because the 95 1500 i had started doing that. Its more or less the same transmission. Anyway, the check valve was sticking and overheating the fluid, yet not enough for me to tell anything was wrong. A lot of the time the TC would go into lockup then drift out of lockup, then back in and back out, over and over and over. Finally the check valve stuck closed one last time for good. $1400 rebuild. You may want to invest in a transmission flush and make sure its MOPAR ATF fluid or you'll be rebuilding that sucker very soon. You may also want to set up a transmission fluid temperature guage. When i had mine rebuilt, i invested in a 24000 lb transmission cooler, a shift kit, and removed the check valve completely. I had no problems after that. The truck is still running strong 100,000 miles after the rebuild. Mine was a gas engine with a lot less torque. If I ever have to rebuild the transmission in my new 2006 cummins, I'll definitely look for a good set of guages, a heavy duty torque converter, and a larger billet transmission pan.

 

My dad's truck had the same problem. A 1999 3500 w/auto. We ended up having to replace a few servos in the tranny to get it fixed. it has been working fine ever since, for about two years.

 

I Had the same with my 97 - 1500 tranny... The torque converter kinda hums... gets wors as time goes by, finally it will jump out of the OD by now the fluid is so hot and it will do more damage within a few miles.
After I had my tranny rebuild , I never used the OD unless I am going over 60Mph... Had it rebuild when it had a 110 K on it.... sold the truck last week with 250 K on it and she still runs like new....

Good luck
Mike

 

You reminded me of something. Kevinc, the transmission will not go into or stay into overdrive if #1 the fluid is too cold or #2 the fluid is too hot.

 

Finally resolved the problem. I removed the throtle position sensor(TPS) and cleaned thewiper and carbon strips. The truck now shifts better than it ever has(I have owned it for about 4 years). I done this about a month ago and it has not acted up once since. ThoughtI would pass this along incase anyone ever ran into this annoying problem.