Hello. I have a 1999 P30 motorhome with a 7.4L and 4L80E that appears to not stay in OD. When fully warmed up in OD range at 55mph I'm at 2500RPM (which is 3rd gear). If I coast down a hill and fully lift off the gas, the RPM drops down to ~1300RPM. As soon as I give it some gas, the RPM...