Power loss

Hi guys. Me again, just bought the wife a disco 300tdi, all fine until on way home today when she went to overtake and lost power, very sluggish when under load (smoke too) will not rev past 4500 rpm, turbo seems to be ok ( spindal turning and blowing when hand over hose) I have serviced it today but with no joy, also checked all hoses and pipes all fine, took exhaust off just incase cat had collapsed but still the same, valve clearance checked and lift pump replaced, when revving the exhaust smells like it's getting too hot!! If that makes sense. Any suggestions?