Hi, Tomb,
I came across a similar situation with my D4D some time back. When I got it, the powershift seemed weak, like it had a sloppy torque converter. It wouldn't even spin the tracks in low when going up against a tree. Trans pressures were fine.
Finally had to pull the thing apart 'cause a engine liner got a pinhole through into the water side.
Pulled the whole transmission/torque apart into little bitty pieces.
The only thing I could find wrong was the torque/trans pump intake screen was plugged nearly solid. The previous guy was a gyppo logger and had brazed up a crack in the torque housing without taking it out of the machine. I presume he drained the oil but the brazing had carbonized a bunch of oil in the torque. It cracked off the inside and plugged the pump intake screen.
I can't say for sure this was the problem in my machine because I haven't got it back running yet but I went through the torque with a fine tooth comb--even bribed a Cat guy (with lunch) to give me the wear limits on the torque to prove to myself it wasn't worn out! The rest of the transmission was fine.
I'm presuming the transmission was sluggish because the torque wasn't getting enough oil into it to make it work properly.
Hope this helps....
Jon.
