Transmission Recommendation

FMX is a fine transmission, I wouldn't swap it unless its broken which would be odd. The 4:10's will make you wish you had overdrive, so if anything, switch to trans that has OD.

I also would definately recommend a quality built AOD (Art Carr, Lentech, ect..) especially with 4.10's. They are built to handle 600+hp now and you'll get the best of both worlds.

i agree with 302 coupe, the fmx is a tough tranny, tougher than the C4 is in stock form. i would recommend that you either swap to a 3.00 gear or an AOD.

I will follow the crowd, and add...

The FMX is a stout tranny is stock form, however there is little to no aftermarket support, and it is VERY heavy.
The C4 can be built very strong, is light, and has a great aftermarket if you need one. There is little to the swap from FMX to C4, however I am like the others, get a strong built AOD. You won't gain any weight from what you have now, and you will cruise comfortably on 3.50-3.70 gears. 3.89-4.11s are borderline too much if your engine isn't built to rev. They can make it feel more like you are driving a truck. Even though the OD would help it in cruising, if you don't need that much gear, then it is kind of a waste in the first couple gears anyway.

2 things:
TCI has a very bad rep for building trannys in quanity, not quality.
AOD trannys are weak in stock form (especially vs AODEs), so get it built right, not stock. AODEs are stronger, but the 'E' means that it requires computer input to function, so it is not the best choice.

Good luck
Dave

There is nothing wrong with the FMX. I would stick with it till it gives out or needs a rebuild.
Kevin

the biggest weak point with the FMX is the cast iron 2nd gear band which can break if you install a stout shift kit. if you don't have a shift kit you won't have to worry about it. there isn't much aftermarket support for the FMX but there is some, art carr and TCI both make mild stall convertors and i think B&M does as well. all 3 make shift kits as does transgo. generally speaking a mild convertor is about all you'll need to do with the fmx if you have an aftermarket cam.

if you're dead set on replacing it then go with a well built AOD. Lentech and Baummann engineering are the permier AOD places. performance automatic has a pretty good rep as well.

if it were me, i'd swap the 4.11's for a 3.25-3.50 gear and keep the fmx.