not necessarily. if you take an efficient convertor, say something like a yank sy3200 compare it to a stock unit, you could gain a few rwhp. but as a genearl rule, you will loose power with a bigger looser stall convertor.

my car which is a cammed stock headed car, only pulled 365 rwhp but traps 116 mph in the cold air.

also locking the convertor is a different story as well.