i have a 2002 3500 with 5.9cumming & 4speed auto. when shifting to overdrive at 35-40mph the converter locksup then disengages then engages at a higher speed. it seems to be worse when the air temp is lower. i was hoping changing the trans fluid & fliter would help. or is normal. any advice would be nice. roube

 

check your grounds make sure they are clean, I had the same problem with my 98.5 and it ended up being the ground from the ECM to the passenger side battery

 

would that be on the batterie or trans

 

I would clean all of them. Mine was the ground from the ECM to the battery

 

thanks for the reply

 

Go over the whole truck and check every ground you can find and clean it. If one is dirty or corroded then chances are others are too. On the highway my truck would shift out of over drive when i started to pull hills so I put a lock up switch on the converter. The switch made and amazing difference but if I don't turn it off before I stop it can stall the truck out and ruin the trans.