Jay-rod427

Some of the MPH loss is mainly attributed to converter slip. A converter never fully locks like a clutch car. OP if you are only running low 12's your car is going to slow down with an auto as it just doesn't have the power to make up for an auto robbing power despite the faster shifts. If you do go auto you may also want to consider re-gearing the rear end as it will seem and be slower off the line.

1fast 99gt

Iam faster then that I traped 130 lol that was my old setup