My RTO-12513 will not go into the high range, (splitter) but starts to grinding upon passing through neutral on the upshift. Once this grinding starts I have to stop the truck to have any transmission gearing. I can't get it to shift either up, or down when this grinding is going on and flipping the splitter does nothing. At a dead stop I can, (in neutral) actuate the range valve hearing a definitive clunk as the range shifts. This also works perfect when driving. When in the high range position, I can flip the splitter button with my thumb and another difinitive sounding clunk is heard. I assume this is normal. However as mentioned, this starts a grinding that does not cease until the truck is stopped, and the range selector is selected back to low range. I've backed up with the range selector in high, and the splitter in low, and with the splitter in high. Although I need to be very ginger with both the throttle and clutch to get the truck to move due to such high gearing, there does appear to be a difference, sometimes. I've been very easy on things as I don't know much about these air shift transmissions and valving. Certainly don't want to hurt anything. The trans drives and shifts fine through the low and high ranges but I've not been able to get the splitter to work on the road since changing the lineset a couple weeks ago. I know the lines are correctly routed as they were changed one at a time. Thanks, Rob