Sorry. My memory fails me...along with a lot of other things.
Hmmm. I thought the 3.4 ran out of steam about 4,500RPM.
My understanding with the 4.9 was that it was good until about 120MPH, but I've never been that fast with a 4.9. I drove one with a 4T60. It was quick, and pissed off the Corvettes, but I was afraid to get on it too hard, for fear of destroying the transmission.
A 3.4
with a stock intake will be starting to get unhappy by ~5K.
I had a Trueleo intake, ported heads and lower intake, FOCOA headers, big injectors, and a Crane 272 cam. It was quite fast, but I spent
way too much time and money to get there.
The stock 3500 in my G6 makes more power (220 HP), right out of the box, than that 3.4 ever thought about making.
The 4T60E is what came with the 4.9, in a car that was nearly 1000 lbs heavier than a Fiero. If it's in a good state of repair, you ain't gonna hurt it, by punching it, if the only difference is that the Fiero is wrapped around it instead of the Deville. You'll probably make a lot more noise, however.