6L80 - 377 gears

[Rocketw19]

I have a 62 impala with an LS3 and matching 6L80 trans hooked up to 377 gears. The car seems like it is launching in 2nd gear. I have almost 500hp and the tires will not brake loose. if I am anywhere other than taking off the car pulls very hard.
I just changed to 377s as I though my gearing was wrong so now I am thinking its something else. My tuner is going to look at the tuning of trans next week but I am impatient I want answers now, lol. I am running 22" wheels in back on 285 tires so they are tall but something is not right.

I found this forum looking for frame info (frame is next)but seen this section and lots of good reply's so decided why not give it a try maybe one of you had this happen before and its an easy fix?

thank you for your time.