SK350 Track Problem

I just got a ditch witch sk350 and the guy i got it from had told me that it had a bad track motor. Since getting it I have removed both the tracks to check the rollers and make sure there was nothing wrong. I replaced the bearings in two rollers. The problem seems to be in both tracks. When operating the unit in reverse the tracks seem to operate normally, it is when I go forward on the controls that the tracks dog down. When I go forward it sounds like the hydraulic motors are winding up. The unit doesnt turn and move like it should, I cant hardly turn the machine at all because of this. When I had the tracks off I operated both controls and the sprockets moved forward and backwards fine (I figured they would with no load on them). I trying to figure out the next step of action to get this machine operational. Any suggestions on what to try next would be greatly appreciated. Thanks

could be several things, ive got a 650 and im not sure all the differences but if the motors are fine going in reverse that would make me think its either in the contol valve or a week pump. still could be the drive motors, can you spin out when you hit a pile or does it stall the engine ? have you contacted ditch witch, how old is it?

we have a 235kobelco and found the shuttle valve on one motor came apart it is located in the brake valve on the travel motor there is an allen plug on each end of the spool and if i remember correctly there is 4 allen head bolts in a cover you remove to get to the spool get a parts breakdown online before you start so you can see what im speaking of.

oops didnt see it was i ditch witch.disregard my bad!!

the sk is a 2005. I did contact ditch witch and there best guess was that the drive was slipping(which didnt make any sense to me since it works fine in reverse) So I replaced the belt and tighten the idler pulley(and no luck) I dont think it would be the the main pump because the attachments and front loader operate fine. I just got the thing and the first thing I did was drain the hydraulic fluid and it was a milky white (which isnt a good sign). When I first start the motor and crank it up there is a window of ten seconds where it moves left and right fine, but after that ten seconds it quits. It wont spin the treds (maybe in reverse). I am thinking about reversing the lines to the control valves and if it works in forward then I will have to assume that it is in the control valves. I am also going to take the some of the main hydraulic lines and blow them out with nitrogen. This thing is pissing me OFF:Banghead I need to find a some schematics for the control valves and hydraulic routing system. The operators manual is pointless for any servicing task. Thanks for the comments it is always a valuable insight to get someone elses opinion. Another problem is that is over 100 degrees in illinois this week and I dont have an air conditioned shop.

Have replaced the sprockets?