Brake Switch as Monza says makes alot of sense. Simply put, the brake switch causes the TCC lock up/release etc. and the brake switch was NOT in the donor car......so the current brake switch COULD in fact be the culprit, as it was not from the original car the engine came from. Nice job Monza, seems as if this is the OP exact issue to fix his dilemma. Hope what you said helps him so he can then go and..... .