I drive a 1986 Trans Am with the stock automatic transmission. I had the transmission rebuilt maybe 3 years ago and it's been a breeze ever since.

Recently i swapped the 305 for a 350 4bbl and left the same transmission, because the horsepower and torque difference really aren't that much.

I got on it today, and it ran perfectly fine right on up to where it should cleanly shift to second, and it just couldn't manage. It kinda choked and bogged down, and it did it again when I retried to launch. It shifts fine when i'm just cruising, but it cannot manage when i'm flooring it. And I've never had this trouble before, I've gunned it a million times without so much as a hiccup.

Suggestions?