Lexs400

I have recently changed the TPS on the 93LS w/trac
the acceleration seems to be smoother now, however it has developed a rather interesting issue.
half of the time, the acceleration is great where the wheels even spin when taking off from stop, at that time the brakes work wonderfully as well, and the temp, speed changes has no effect on this phenomena.
the rest of the time, the acceleration suddenly becomes sluggish, acceleration drops to half of what it is and at that same time the breaking power drops considerably where I have to almost apply twice the pressure on the brake pedal to stop the car.
i am coninced that it is more of an electrical component issue than a mechanical issue. however I would like to know what part needs to be looked at to trouble shoot this.
there are no error codes in the ecu at the moment.
thnx in advance.