My 2000 RR is slow to change into 4th. I have changed the pickup filter and the box does not slip in 4th when it eventually does change to 4th.

I am thinking that there may be an electronic fault such as the box does not know throttle position but then again, it changes in the lower gears quite normally.

Does anyone have any ideas before i clean the valve block?

 

You don't want to mess with the tranny, there are no adjustment since it is completely controlled thru the tranny ECU by the ECU.
How many miles on the truck, how often do you change the fluid and at what speed does it lshift into 4th and lock up the torque converter?

 

It's done 134,000 miles and it varies at what speed it changes. When cold it will change and lock up at about 40 mph but this goes to 50 ish when hot.

I have changed the fluid and all was comlpetely normal as i drove away for the 1st time but the problem came back after five miles or so. Last change of fluid was about 500 miles ago, i used Dextron 3.

you can feel the system trying to change if you slowly accelerate between 35 and 45.

On occasions it actually changes up if you go from light throttle to increasing throttle opening just as you start up a hill.

 

You might want to throw a bottle of Lucas tranny additive in and give it a try. Best thing I have found to help free up sticky valve bodys.

 

Yes, good idea! I've ordered it, I'll let you know how i get on.