ok right now ive got a jegs 2300-2700 12" converter in my th-350. the problem is i can only footbrake it to about 1800. would this be because my motors not making enough torque?? do I need to step up to say a 10" 2800-3200 to make it even flash to 2500?

heres my motor specs-

307
stock internals
"601" 305 heads
9.5:1
crane energizer 274h cam
performer rpm intake
600 edelbrock
1 5/8 headers
4.10 gears

I was thinking of either going with 10" acc "boss hogg" 2200-2800 or the 2800 3200. or the red neck performance 10" 2200-2500
only want to spend about 200