The 950 may have a worn pump, or the P1/P2 pressures may be low due to weak springs or poppets and slugs in the transmission shift valve stack. So, assuming your oil looks good and the filter & the tranny magnetic screen don't show any signs of a major problem in the form of excessive seal material or fragments and steel or clutch debris, what you need to do is test the P1/P2 pressures and see if they are within spec. If they are, and pump main pressure is OK, then your problem is likely due to normal wear on the seal rings for the forward/reverse clutches.
One other thing is the viscosity of the oil you are using in the tranny. If you are using 10wt., then as I mentioned before, it may take some warming up first before the seals and other thingies expand and seal properly. You might try some 30wt,, and see how that does. Some folks use 15W30 or 15W40 in their trans, but I do not recommend it. It's more expensive and the tranny doesn't need a multi-vis oil in most cases, unless you are working in a cold climate.
If you are already using 30wt., the same problem may exist, only it's the oil that needs to warm up along with the sealing parts. This will more likely cause the trouble in the valve stack. On the other hand, worn slugs, poppets, and valve seats can cause this too. The P1/P2 tests will help to pinpoint this area.
Sometimes, in the Cat clutches that I've worked on, you see a buildup of debris in the seal ring at the very bottom of the piston and housing, meaning as the trans is standing upright, this would be the bottom of the piston as it sits in the bore. Quite often this results in a groove being worn in that spot and it will leak pressure untill things warm up and the cavity get fully pressurized after all the voids are filled. The seal gets badly worn too from all the dirt and stuff and once it's gone, it has to be replaced, no easy job I'm sorry to say.
Hope this helps. Good Luck!
