On stock 91 GT - question on OEM cat system -

Not going to make any difference on the engine cooling, I'm on the fence with trans coolers, your trans needs to run about the same as engine temp, at least that is what I've been told by a trans 'expert' so may be detrimental in cold climates, I think the jury is out on that one though.
the 'dump truck' runs duel coolers cause it pulls a lot of weight.