what % is your pump motor running at? Does sound like a 4th valve issue but why not check. Also if this is a new machine to you the manual is a bit light on the oil required to fill the tank after cylinders have been moved. I added another 50ml + after I initially got things running. Saw some air in the lines and could hear it sucking for more fluid. It could be a mixing issue on the TX, I don't have the 4 valve block but think there is a thread on here about adjusting it. Mainly making sure your Aux 3 (F mode) is at the "N" position(not 100% on that) and possibly adjusting your pit trim knob.
Maybe this one?
http://www.rctruckandconstruction.co...ghlight=4200xl