Transmission advice... FMX 3spd auto... BUSTED!

[jkucyj]

So someone thought it was a good idea to bolt up an FMX 3spd out of a 72 Tarino to my 352 in my 66 Galaxie. It is a POS. I do like the gearing but I'm loosing alot of power. I don't know if it's the trans or maybe I bought a bad tq converter. It's a stock tc.
1. Trans takes a good couple sec to get in rev
2.Has a hard time shifting into 3rd sometimes 2nd as well
3 Never drops back down to 1st at stop lights, it will leave the light in 3rd unless I downshift manually
4. I can tell it slips under heavy throttle
5. Has good vac and new modulator valve...Fluid level is good hot in park and N

I found a master rebuild kit for under $100. AAMCO quoted $350 for a rebuild and I want a 2400 TCI Breakaway stall converter $377. for a total of around $850. I can't stand this. I know I have more power but can't get it to the ground. I'm guessing it's somewhere around 250whp. My Holley is going to be replaced with a quick fuel as well. I should have at least 350hp hitting pavement. I've felt it hit 2 times when it seemed to act right and it was a whole different car.
Question is.... Is this just a bad TC? I don't think so, but I'm not really a trans pro.
Of course I'd rather a C-6 but..... I like the long gears for some reason. I think the FMX has potential. If I run into the money to build the motor the way I want, I'll have an indestructible trans behind it. But for now a rebuild is sounding good.
So... trans, TC or both?
And thanks for reading.