i have a 2003 chevy silverado 2500hd 6.0l with the 4l80e i believe. 125k miles. on the highway at 75mph im turning about 2500 and at 80mph almost 3000rpm. (im pretty sure the speedo is correct) the truck has the stock 245 tires and i have a 410 rear. something has to be wrong there is no way it should be that high. any thoughts? i was thinking the torque converter is not locking up is there anyways to test it? i just serviced the trans (flush and filter) and still no better the truck drives and shifts fine the fliud was very dirty just bought the truck and the previous owner neglected some stuff unfortunately. any advice would be great.
thanks
Brendon

 

What you could do is drive down teh road at 70 and pull the shifter down to 3rd. See if your RPMs increase. Then shift it back into over drive and see if the RPMS change again. Also you could as you are driving push on your brake pedal a bit and see if your RPMs increase. This will tell you if the torque converter is locked at cruising speeds. If it unlocks the RPMs will increase slightly. What was it doing before you did the fluid and filter change. And you could take it to a tranny shop and most shops will do an on road diagnostic for free.

 

3000 rpm at 80 mph with a 410 rear is about right.........what about the tow/haul switch? check the wires and make sure they are not cut....typical problem.

 

i have a 2000 model 2500 series with the same trans. The torque converter started unlocking (would lock up when oil was cold, but as soon as trans warmed up it would unlock. at first i thought is was shifting out of overdrive, but when torque converter locks up you see tach lower and it feels like it just shifted into another gear.

Some type seal had given away in torque converter and it could not hold oil pressure to stay locked in, the torque converter had to be replaced at 75K. Cost me $1000 but truck has ran fine since, truck now has 92k.

when mine would unlock the shifts would be harsh hard shifts. you could stop, turn off motor then restart and it would shift and work fine for a short while,
Trans tech said the computer was reseting when i turned off motor, but after a while that would stop working, the hard shifts was the computer sencing a trans slippage and was increasing the hyd pressure to keep the clutchs from slipping.

all i know is a new torque converter fixed the problem.
works good now.

 

thanks for all the help. the tow haul mode does work ive checked that and also checked while driving dropping it down to 3rd and the rpms do increase i will have to try the brake pedal one. the truck drives the same as before i did the trans service.

 

You just proved that it is locking up.....remember this is a 2500 with 410 rear end...you are gonna run a little bit higher rpm than say a 3.83 rear.

 

thanks for the help. i just thought that was too high i guess the trans is ok though

 

2003 2500hd with 6.0. I'm having the same problem with mine, it runs 2300 rpms when in overdrive properly at 70 mph. Then it will jump the rpms up 2700 on the rpms for no reason and stays there for awhile . Then latter it drops back down to normal 2300 rpms. I've had the tranny rebuild and it still does the same thing. I can not firgure it out. Anything help you out?

 

I have a 2003 1500hd 6.0l with the same trans problem. Seems like the torque converter will randomly unlock from direct drive, then a short time later (usually a few miles down the road) it will lock up again and run normally. Any ideas? The local shop in town told me I have a misfire and it could be that, so I went through and replaced plugs and wires with no change.
Thanks

 

Check to see if you have any exhaust manifold bolts that are broke off. It is common of them to break off and this will give you a misfire code.