Just swapped my car to a m6 a few weeks ago. Only has maybe 70 miles on it so far. I just got the pcm re tuned but I noticed the sluggish feeling before. It originally had a 2800 FTI converter and stock 3.23 gears in it prior.

It just seems like the car is a dog in all gears now. Not a lot of torque or power except for the top end of first gear. I just don't get it. Are the 3.23's that bad for the t56? Lol. It seems like thats what I'm leaning toward but I'm thinking 3.42's aren't that far away to make THAT much of a difference. I swear my car was faster with a slipping transmission. Felt great with the auto in it despite the bad trans.

Any ideas?? Or was I just used to the instant torque of a converter? Any theories would be great. No SES light as well.

 

3.90 gears now. You had a 2800 that let the engine sit in a nice powerband spot with even small amounts of throttle. Now you have a gearing mismatch; if you're not FI, 3.23 and that trans. aren't a match.

A GTO ratio trans. would help a bit, but 3.90s with your existing is a good match.

 

I agree. I wnet from a stock stalled auto with 3.42s to m6 and it felt quicker especially since the shift drop wasnt as extreme, A stall will hide that though. With 3.90s in mine now it screams

 

Ok, so most likely rear gear ratio mis-match? I can cruise at like 2800 rpm on the highway in 4th gear right now. Lol I'm still breaking in the clutch so I haven't got on it that hard since it still chatters and stuff. but i can tell the low end torque sucks right now!

Just a LT4 hot cam, exhaust and LS1 lid are my only power adders.

 

An M12 w/ 3.42's (C5Z06) is just about the same as a normal M6 (T56) with upgraded 3.90 until 3rd gear. 3rd-4th in a Z06 has a massize drop-off of RPM's and the M6 with 3.90's doesn't have near the drop-off. 3.90's will be perfect with your combo!

 

my 6 speed bolt on car has stock 342 gearing and had stock 10 spokes with 245/50/16's on it when I got it . Swapped to 295/45/18's which are 28" vs 25.5" for the 245/16's and it by no means made it a dog - did the math and its approx. equivalent to swapping gears to 308's (10%) you have something else going on....
its not that 323's cant work with a 6 speed

I would say your tune would be the first place to look , who tuned it and did they have the car present or mail order?

I went back and looked at your mods and seeing its cammed tune is very important and it will like more gearing anytime you add a cam so in your case cam/6 speed/highway gears arent ideal