[lukecp]

If you want to cruise 90 and still have good low-end acceleration, a 700R4 or 200R4 automatic would be the way to go for an auto tranny. The 700R4 has a low 1st gear (3.06:1 compared to 2.52:1 on a TH350), and has a .70:1 ratio overdrive, which will allow you to travel 30% faster at the same RPM you are turning in high gear right now.

The 200R4 has seveal advantages over the 700R4, but can be more difficult to find and some say it is a waker tranny. The 200R4 has a higher 1st gear than the 700R4; it is 2.75:1. That isn't really a bad thing though. The RPM drop off between 1st and 2nd gears on a 700R4 is pretty bad, about 50%. So if you are turning 5,000rpm in 1st gear, when you hit 2nd, your rpm will drop to 2500, and uless your motor has alot of low-end power, it may slow you down a little bit. The 200R4 has about a 45% rpm drop off, so it isn't quite as bad.

I would call a local tranny shop, and ask for a price on a rebuilt unit for either the 200R4 or 700R4. There is a post on converting to a 700R4 on the FAQ board.

Also, your floor won't have to be cut with either tranny.