Cat 955H slips when pulling uphill

Does anyone have an idea why a 955h would slip when going uphill? It will go uphill backwards just fine but when you try to go forward it will pull for a second then slip for a second. It acts like it is low on fluid or maybe not getting fluid to the pump all the time. I don't have a manual and I am not sure where to check for filters and I'm not sure which stick is the transmission fluid. It has two dipsticks and I'm not sure which one is the fluid to the powershift. I added a little 30 weight non-detergent oil to one that was low and they all seemed to have enough in them. It is a lever steer model and serial number 60A5840. Thanks for your help.

Don't mean to ignore you but you need to do more to help yourself. You need to get a set of manuals and familiarize yourself with the machine and its maintenance requirements, then we will be glad to help with problems.

A frist simple check would be to check the transmission oil level ,dipstick nearest the front of tractor .Check oil level with machine on level ground ,oil warm ,engine running at idle ,and trans in neutral .
Non detergent oil is a no no ! Proper oil should be 30wt oil with a CD or CF rating

To me that would mean the forward clutch pack is slipping I guess it does in both forward gears. I'm pretty sure that has cast iron piston rings. Before I got too serious going inside il'd make sure the pressures were up. Speed clutch PSI 270-300 Directional clutch PSI 215-245. I have had on occasion that the o-rings on the connection tubes from the valve body to the clutch assembly were bad and there is plenty of them in there, if you go that route make sure they are the yellow ones. If someone has been in that transmission before and used black ones they get hard and crack from the heat. That was an easy fix compared to pulling the tranny. Everything was crammed in tight places it took a lot of patience (which I sometimes don't have).

Good Luck
Maurice