the elevator reached the up stop and the nose down pitching
- a bit puzzled by this - are you saying that you did not actually 'stall'? If the nose dropped with further speed reduction and full up elevator that might suggest the elevator travel/effectiveness may perhaps have caused the difference and it was loss of pitch control you saw rather than an aerodynamic 'stall'. Certainly in 'text book' air test stalls in 737s one often reached full nose up tail authority before classic stall symptoms (buffet,
marked nose or wing drop) appeared.
Yes, I reckon the effect of 100rpm's-worth of propwash could affect pitch authority.