ABL262: If you could talk to the (now defunct) CAA Flight Department, which used to monitor fleet climb performance based on CofA renewal flight test data, they would have shown you a graph of a steady decline in performance over the past ten years. In RAF days there was no hesitation to change engines, either for defect or immediately on life expiry. In civvy street, engines flog on and on, way over the Lyco TBO (unless operated commercially). A further risk to civvy engines is that many of them have very low utilisation compared to the Dog's time in the military, resulting in heavy internal corrosion and excessive wear, especially of the camshaft. This has a marked effect on the power developed by the engine.
However, people often forget the importance the propeller, not only making sure it is correctly adjusted, but also the effect of years of blending and cropping at the tips due to stone damage operating off grass strips and crumbling WW2 runways. A new Hartzell prop tip is something of a 'paddle blade' and it does a lot of work soaking up the engine's power. Crop or blend that tip (even within R&O limits) and there can be a significant loss of performance.
A blended prop even within R&O limits, which are usually based on sustaining structural integrity of the prop, on a clapped engine may therefore not develop enough grunt for the aircraft to meet its book figures. Already several Bulldogs are carrying performance write-downs in their Flight Manuals because they can't get within the 70 ft/min drop off on the book climb figures allowed by the CAA.
From what everyone here is saying is that the Bulldogs used to whizz along in military service, so the performance drop-off must be a civvy thing. Chaps, look to your engines and propellers.