So very stuck...

My timing at idle is about 24* with 36-38* overall, I also just checked my TV cable and found the the TV port still has about 1/4 inch travel still left in it at WOT on the carb. The flex plate is in good condition and the torque converter as well. We just installed this transmission 2 months ago. And I was getting this issue just before we rebuilt with the manual transmission that was in it. I'm wondering if the play in the TV cable is the motor fighting the transmission as the line pressure may not be reaching its max. But that seems odd as this was a problem with the manual trans as well which is why I moved to an automatic ( also driving in heavy austin tx traffic daily was killing my knees) in the first place. Any ideas on how to ease the detonation if that is the issue?