I have a 96 3500 dually with manual. 149k miles on it. at 144k I had its 4th clutch plate put in ( I tow over 13k lb horse trailer with it). For the last few hundred miles it grinds when I go to 3rd gear unless I am going under 15 mph, then it is ok. grinding seems to gradually be getting worse. Whats the prognosis? FYI , i'm a family doctor , not a mechanic. should I get it fixed now or wait? planning on buying a new 3500 when the 2010 models come out.