Does that plane have a ferry tank installed!? Either they are REALLY heavy or their engine isn't developing full power. The climb rate seems low and the takeoff run was really long.
In the good old days the UK CAA would conduct an air-test at each 3 year CofA renewal; part of the test was to check that the stall warner was within tolerance (+/- 4 knots?). If outside these parameters the stall warner could be repositioned by moving it on the slotted holes and the aircraft retested. However, if the stall warner itself was faulty, the cost of replacement would make you weep.
