its all about the power/tq. traction has always been great. leaving on 8# boost, just really rich holding power back

 

I bet some lower gears would help you out, Im going to try some 3.90s I think.

 

I can't w/28" tire. crossing traps at 6300rpm now. that's right at max power on dyno.

 

I've got the same off the line issue as you. I'm in the middle of going from 3.42s to 4.10s in my 14 bolt to get my pig off the line better. I run 28" M&H's and hopefully will be crossing the line around 65-6600. If a little higher I'm not worried.

 

You may want to look at your converter as that seems like a lot of slip. With 3.42 gears, directly coupled, 123mph should be around 5Krpm and 6300rpm should be around 153mph. That's a 20% slip at the traps.

 

I've calculated the converter slip also and I know 15-20% is on the high side even for th400. probably pushing converter pretty hard, only rated for 800hp. tranny temps never over 190 though. i'll wait til 4.8 lets go and get a better converter.