What are you running in the 468? Thirteen is about the best the '70 got before the rebuild. 402 with stock 063 heads, cast iron Q-Jet intake, Q Jet, LS6 cam, headers, and 3.31's out back. Depending on how big your cam is it may not like the low RPMs of the 2.73's at all. That may be part of the problem. Just a thought.