Can't answer if your wastegate is malfunctioning but on many fixed wastegate turbos with constant speed props, the prop efficiency climbs during the takeoff roll and the MP creeps higher as speed is gained because the prop isn't working as hard.
If you had a need for absolute full power for a takeoff in the Turbo Seminole you'd push until you were about 2" below overboost and then leave it there. By the time you were airborne you'd be flirting with overboost.
Which is why on the checklist the owner had a normal-takeoff MP number and then listed the Max below that for maximum performance. We usually took off about three to four inches below overboost to give the system the ability to rise and not actually hit the overboost light, if plenty of runway was available.
If you really wanted every last bit out of it I suppose you could go right up to just below overboost and then start easing it back as the speed came on, but you'd have to have some time in the thing to know how quickly that would happen and keep coming back with it as you took off and climbed out, gaining speed.
Doing the ME CFI ride in that thing and prep, one of your jobs was to keep the overboost from happening. Almost every student would "touch" the light sooner or later during some maneuver. OEI approach and they need more power, landings in gusty conditions and they need more power, inattentiveness on a takeoff, something. You were always on guard for it and ready to either verbally correct it if it was mild, or physically grab their hands and pull the throttles back if they really were headed for overdoing it.
Even DPEs will ask the owner to remind them of the limits the owner likes before heading out with someone for a checkride. Nobody ever wanted to hurt the airplane. Real easy to do with a fixed wastegate system like that.
