Too much gear?

I run the MP 296/.557 in my 360, Eddy heads, M1 intake, 750DP Holley, in my Barracuda, 4.56 gears, 28x9 Hoosier slicks I trapped 11.14 at 120.27mph, don't remember what the RPM was.

Crunching numbers says I crossed the line at 6584 rpm.

Granted, I got more cylinder head on my combination; I don't think it would account for a 22mph difference, plus the fact you lost 4 mph relative to your old .508/280 combination.

As a guess of what to do, up your shift point.......the .557 is gonna peak power higher in the rpm range, get up there and use it.